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Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)
	Technical Chapter 13: Classification
		13.1 Set of rigid screens
		13.2 Screen riddle, vibrating screen
		13.3 Cantilever grizzly
		13.4 Sizing drum, classifying drum
		13.5 Cone classifier
		13.6 Countercurrent hydraulic classifier
		13.7 Hydro-cyclone
		13.8 Log washer, spiral classifier
		13.9 Rake classifier
		13.10 Sluice, sluice box, washing sluice

Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)

Technical Chapter 13: Classification

13.1 Set of rigid screens

Mining General
Beneficiation, Classification

engl.:

screening gate, grizzly

germ.:

Siebklassierung in starren Sieben, Durchwurf, Reibgatter

span.:

clasificacion en tamices fijos, clasificacion por tamano en tamiz

TECHNICAL DATA:

Dimensions:

starting at 30 × 40 cm screen area for single screen, up to 2 × 2 m for coarse screens (grizzly)

Weight:

starting at 5 kg per screen

Extent of Mechanization:

not mechanized

Form of Driving Energy:

manual feeding, possible manual drawing as well

Mode of Operation:

semi-continuous

Throughput/Capacity:

very dependent on grain-size of feed

Operating Materials:

Type:

water for wet screening

ECONOMIC DATA:

Investment Costs:

example: for three screens 300 DM

Operating Costs:

labor costs only

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Location Requirements:

water availability

Grain Size:

100 ym up to several decimeters separation cut-off size (screen openings)

Special Feed Characteristics:

no clay-containing' sticky material

Replaces other Equipment:

other classifiers

Regional Distribution:

worldwide

Operating Experience:

very good |————|————|bad

Environmental Impact:

low |————|————|very high

Suitability for Local Production:

very good |———|————|bad

Under What Conditions:

frames are very suitable for local production by carpentry or metal workshops; screens are generally imported since they are subject to extreme abrasive forces and must therefore be constructed of high-quality material.

Lifespan:

very long |————|————| very short

Bibliography, Source: Stout, Schennen, Stewart, Priester, Reitemeier, Villefosse, Gaetzschmann, Cancrinus

OPERATING PRINCIPLE:

Screen classification with rigid (stationary) screens can be performed either wet or dry. Dry screening is applied for dry coarse-grained material and occurs in an inclined screen. Wet classification is conducted in "screening gates", or a series of successive stationary screens built into a sluice or trough, sequentially going from coarser to finer screen openings from the top (feed end) to the bottom (discharge end) of the trough. The screened unders are transferred to the next (one degree finer) screen via the processing water.

AREAS OF APPLICATION:

For classifying material of coarse and medium granulation prior to its entering the main separation facility.

SPECIAL AREAS OF APPLICATION:

Selective classification of products from sorting and comminution processes.

REMARKS:

The dry screening process with the inclined screen is disadvantageous in that it has a low separation precision as a result of undesired separation of adhesive grains.

Wet screening in rigid screens and distributing the material over the screen by means of a spatula leads to inhomogeneity in the slurry comprised of the screened unders. When the classification processes, which are sensitive to changes in the feed slurry, directly succeed the wet screening, then special equipment (such as pinched sluices) for homogenizing the slurry flow must be placed between these two steps. Screens were already being applied in antiquity in Greek mining. For acidic process water, it is absolutely necessary that the bottom of the screens be constructed of stainless steel or plastic. During wet screening, care should be taken to either catch the fines in sedimentation basins, or immediately separate them in sludge ponds, to avoid high losses of valuable minerals.

Grizzlys, used for coarse-material separation, should be installed with a minimum inclination of 25° - 30°, allowing the coarseest fractions to roll down the grid and be collected for subsequent crushing.

SUITABILITY FOR SMALL-SCALE MINING:

Wet screening is a low cost, simple, quick and precise alternative for sorting feed material of medium to coarse grain-size. Especially when only smaller quantities of feed require processing, a mechanized classification is not necessary.

Fig.: Screening gate or screened grid-washer for wet classification with rigid screens. Source: Schennen.

Fig.: Simple hand screen with sprinkling device. Source: Stewart.

Screening gate for wet classification of course-grained material. Clearly visible are the outles for the screened unders , wich then directly enter the next (finer) subsequent sorting step; Mina Candelaria, Sud lipez, Bolivia.

Fig.: rigid, fixed grate for separating out large boudles, made of rails. Source: Stout.

Wooden grizzly for separating coarse coal underneath an unloading ramp for end-loading mine cars; Colliery in Region Rio Checua, Cundinamarca, Columbia.

13.2 Screen riddle, vibrating screen

Mining General
Beneficiation, Classification

germ.:

Ruttelsiebe, Schwingsiebe, Ratter

span.:

criba vibradora, instalacion de tamices con movimiento circular

Manufacturer:

Schenk, Jost, Mogensen, Eduardo, INCOMEC, Milag, Met. Cancha, Volcan, Alquexco, Eq. Ind. Astecnia, IAA, INCOMAQ, COMESA, FAHENA, Telsmith, FIMA, FAMINCO, Famia, fund. Callao, H.M., MAGENSA, MAENSA, MAEPSA, Met. Callao E.P.S.

TECHNICAL DATA:

Dimensions:

from 30 × 40 cm upwards, 10° - 20° inclination, 80 - 100 min-1 vibrating or shaking frequency

Weight:

from approx. 50 kg up to several thousand kg

Extent of Mechanization:

fully mechanized

Power:

low, maximal 1 PS/m² screen area

Form of Driving Energy:

hydromechanic impact mechanisms, manual impact mechanisms

Alternative forms:

pedal drive

Mode of Operation:

continuous

Technical Efficiency:

comparably higher than that of rigid screens

Operating Materials:

Type:

water

Quantity:

60 - 80 % by volume of feed quantity

ECONOMIC DATA:

Investment Costs:

manual, starting at 100 DM per screen when locally produced

Operating Costs:

usually labor costs only, possibly energy costs

Related Costs:

drive system

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————————| high

depending upon degree of mechanization

Maintenance Expenditures:

low |————|————| high

the removal of adhesive (sticky) grains in the feed is necessary

Location Requirements:

water availability

Grain Size:

> 50,um up to < 50 mm

Replaces other Equipment:

rigid screens

Regional Distribution:

not known in semi-mechanized processes in small-scale mining in Latin America; only used for wet classification in Jig operations

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under What Conditions:

wood and metal manufacturing shops

Lifespan:

very long |————|————| very short

Bibliography, Source: Calvor, Agricola, Fischer, Schennen-Jungst, Liwehr, Villefosse, Delius, Gaetzschmann, Rittinger, Cancrinus, de Hennezel, Gerth

OPERATING PRINCIPLE:

In contrast to rigid, fixed screens, the bottom of vibrating screens (screen riddles) oscillates either longitudinally or laterally, shaking the material on the bottom of the screen and enhancing the flow through the screen openings. This results in a separation between the oversized (screen overs) and undersized (screen unders) grain fractions.

AREAS OF APPLICATION:

Dry or wet classification of coarse, medium or fine-grained feed fractions.

REMARKS:

Deflection with vibrating screen 55 - 80 mm
Deflection with impact screen 25 - 55 mm

The space requirement for vibrating screens is much less than that for rigid screens. Colotten placed underneath the screens for catching the individual fractions allow the screens to be staggered vertically on top of each other.

Car springs can be used as shaking devices and buffers.

Optimal ratio of screen length to width is approx. 2.7: 1

SUITABILITY FOR SMALL-SCALE MINING:

Even slightly-mechanized forms of vibrating screens are preferable to rigid screens due to their higher efficiency, lower space and water requirements, and finer degree of separation.

Fig.: Manual shaking screen. Source: Cancrinus.

Fig.: Operating principle of a vibrating screen (left) and impact screen (right). Source: Treptow.

Fig.: Self-vibrating screens made of railroad rails which start swinging upon impact of the feed material. Source: ITDG.

Fig.: Multiple-step screen riddle. Source: Liwehr.

Fig.: Two-step impact screen. Source: Schennen.

13.3 Cantilever grizzly

Mining General (pit and quarry)
Beneficiation, Classification

germ.:

Antriebslose Schwingsiebe

span.:

criba vibradora sin fuerza motriz (parrilla)

Manufacturer:

Mogensen

TECHNICAL DATA:

Dimensions:

separable grain-size cut-off: 25 - 40 mm minimum, approx. 300 mm maximum

Weight:

from approx. 200 kg

Extent of Mechanization:

not mechanized

Form of Driving Energy:

uses impact of falling feed material to induce shaking

Alternative forms:

as vibro-sizer for material that is very difficult to screen, but then mechanized

Mode of Operation:

continuous

Throughput/Capacity:

> 100 t/h

ECONOMIC DATA:

Investment Costs:

minimum of 20.000 DM fob location of manufacture in Germany

Operating Costs:

very low

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Location Requirements:

none

Grain Size:

< 1000 mm

Output:

precise screening

Replaces other Equipment:

vibro-screens

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very |————|————| good bad

Under What Conditions:

Mogensen holds a patent for its product "rod-sizer". Other forms of powerless self swinging screens can be locally constructed from old rails or by using old drilling rods.

Lifespan:

very long |————|————| very short

Bibliography, Source: Company's Information, Mogensen

OPERATING PRINCIPLE:

Screening occurs through the use of one-sided and divergently attached rods, inclined so as to allow the feed material to flow over the "grate". The impact of the material flowing over the grate causes the rods to swing, which in turn prevents the grate from becoming clogged.

AREAS OF APPLICATION:

Coarse screening prior to coarse crushing Screening of gold-containing conglomerates Screening of coarse coal Classification of construction material in industrial minerals (pit and quarry) operations

REMARKS:

For local production, old drilling rods are very suitable; they are inexpensive, very resistant to wear, highly elastic and available on the local market.

The lower separable grain-size limit lies around 50 - 100 mm.

SUITABILITY FOR SMALL-SCALE MINING:

For non-mechanized coarse-grain classification, the "rod-sizer" is very suitable for application in vein ore mining, In alluvial mining and in pit and quarry mining due to its high throughput and simple construction.

Fig.: Non-powered "rod-sizer" for coarse screening. Source: Mogensen company information.

13.4 Sizing drum, classifying drum

Mining of partly consolidated loose material
Beneficiation, Classification

germ.:

Klassiertrommel

span.:

tromel clasificador, criba rotativa

Manufacturer:

Milag, Met. Lacha, Alquexco, IAA, Buena Fortuna, FAHENA, FIMA, MAGENSA, MAEPSA, Met. Callao E.P.S.

TECHNICAL DATA:

Dimensions:

18 - 25 min-1 rpm, circumferential speed < 1 m/s, diameter 2 0.5 m, length 2 m for single drum with three sizing grades

Weight:

starting at approx. 100 kg for smaller types

Extent of Mechanization:

semi-mechanized

Driving Capacity:

starting at 0.5 kW

Form of Driving Energy:

hydromechanic

Alternative Forms:

internal combustion engine, electric drive, manual operation for small models

Mode of Operation:

continuous

Throughput/Capacity:

minimum 1 t/h;

for dry screening:

0.27 t/m²h per mm screen opening

for wet screening:

0.45 t/m²h per mm screen opening

Operating Materials:

Type:

water

ECONOMIC DATA:

Investment Costs:

starting at approx. 1500 DM

Operating Costs:

mainly energy costs

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Location Requirements:

water availability

Grain Size:

< 50 mm

Replaces other Equipment:

screens and vibrating screens

Regional Distribution:

locally applied in small-scale mining in Latin America

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under What Conditions:

good-quality perforated plates or screens must be available on the national market

Lifespan:

very long |————|————| very short

Bibliography, Source: Gerth, Priester, Treptow, Fischer, Callon, Stifft, Schubert, Rittinger

OPERATING PRINCIPLE:

The sizing or classifying drum is a mechanized form of wet screening in which several screens or perforated plates (arranged finer to coarser from intake to discharge) are aligned so as to form a drum. The drum is rotated by an external belt-drive transmission. The material moves from finer to coarser screens, during which the undersized grains are discharged via cones and distributed to the various sorting devices, such as hand jigs or sludge ponds.

Water is sprayed after 100 to 120 degrees rotation (from deepest point) to clean the screens and improve material transport.

REMARKS:

The sizing drum is characterized by its highly synchronous operation. The throughput quantity greatly depends upon size of the screen openings, with coarser screens delivering a higher throughput. Double-shell or triple-shell screens require less electrical energy and water consumption, have higher throughput, and are subject to less wear. Reference has also been made to manually-driven classifying drums (Stifft).

Two different types are in operation:

- drums with cylindrical screens and inclined axis and
- drums with conical screen housings and horizontal axis

Angle of Inclination: 4° - 5°

Lifespan: with wet screening up to 20.000 t throughput; with dry screening up to 100.000 t.

The disadvantages of sizing drums are the comparably high energy consumption and low self-cleaning effect

To process tenacious, sticky or clay-containing materials, a preliminary sorting with a screenless drum-unit, equipped only with catchers, should be performed. In this unit, the material is precrushed autogenously.

Drums constructed without an axis also exist. Such drums must have a load-bearing housing which also enables the load to be carried on rollers (such as, for example, four car wheels), a construction which then permits a simpler drive-system design,

SUITABILITY FOR SMALL-SCALE MINING:

Sizing drums are most suited in small-scale mining for classification of coarse and medium-grained feed material. Advantages lie in the high throughput quantities, continuous mode of operation and low space requirements.

Fig.: Concentric multi-step drum with conical screens for easy screen replacement. Source: Treptow.

Figures

Fig.:Conical sizing drums, above with screen housing, below with concentric screens. Source: Fischer.
Fig.: Conical drum: longitudinal and cross-section views. Source: Treptow

Fig.: Double-shelled drum. Source: Gerth.

Fig.: Construction for inserting screen plates into a concentric drum. Source: Treptow.

13.5 Cone classifier

Mining General
Beneficiation, Classification

engl.:

box classifier, settling box

germ.:

Spitzkasten

span.:

clasificador de caja en punta, caja en punta

Manufacturer:

FIMA

TECHNICAL DATA:

Dimensions:

from about 1 × 0.8 × 2 m up to several m in width and over 10 m in length

Weight:

from approx. 40 kg

Extent of Mechanization:

not mechanized

Form of Driving Energy:

only processing-water current

Mode of Operation:

continuous

Operating Materials:

Type:

water

Quantity:

slurry with < 40 % by vol. solids

ECONOMIC DATA:

Investment Costs:

approx. 200 DM when locally produced

Operating Costs:

labor costs only

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Location Requirements:

water necessary

Grain Size:

fines up to 1 mm

Output:

Separates into several different grain-size fractions, for example a 3-chamber settling box into 3 distinct fractions plus fines. Settling-box classification leads to more precise separation results in later processes (concentrating tables, sludge ponds, chutes, etc.) than does screen classification.

Replaces other Equipment:

screen classification

Regional Distribution:

rare

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under What Conditions:

simple carpentry workshop

Lifespan:

very long |————|————| very short

Bibliography, Source: Treptow, Quittkat, Priester, Callon

OPERATING PRINCIPLE:

A cone classifier or settling box is comprised of several settling chambers, in the form of inverse pyramids, with outlets at the bottom. The slurry-feed flows through this series of chambers, and depending upon the retention period, intake and discharge flow velocity, volume of the settling chamber, etc., specific grain fractions settle out onto the bottom of the chamber (according to the principle of equal settling velocites) and are removed. The remaining slurry flows into the succeeding basin, where the next finer fraction is separated via sedimentation.

AREAS OF APPLICATION:

Classification of medium and fine-grain feed material for subsequent processing in hydromechanic gravimetric separating facilities.

REMARKS:

- lost fines can be avoided by the use of a back (underscreen) water flow (settling boxes with clean water countercurrent)
- the walls have > 50° inclination
- Rittinger provides the following dimensioning and calculation guidelines:

Per m³ slurry input per minute, the following dimension relationships for single chambers are applicable:

Slurry flow should be approx. 45 l per minute and m water surface.

No.

width

length

� discharged material

1

1 m

2 m

40 % of the weight

2

2 m

3 m

20 % of the weight

3

3 m

4 m

18 % of the weight

4

4 m

5 m

10 % of the weight

in sludge overflow 4 %

SUITABILITY FOR SMALL-SCALE MINING:

As non-powered fine-grain classifiers, settling boxes (cone classifiers) are very suitable for small-scale mining beneficiation of fine material due to their sturdy construction, continuous mode of operation and low investment costs.

Fig.: Wooden cone classifier (settling box). Source: Priester.

Fig.: Cone classifier (settling box). Source: Treptow.

Fig.: Cone classifiers and cone classifier with fresh water countercurrent. Source: Quittkat.

Fig.: Cone classifier with countercurrent. Source: Otero.

13.6 Countercurrent hydraulic classifier

Mining General
Beneficiation, Classification

engl.:

chamber classifier

germ.:

Aufstrom-Hydroklassierer, Kammerklassierer

span.:

hidroclasificador de corriente ascendente, clasificador hidraulico, clasificador de cameras

Manufacturer:

Denver Peru, TMM Potosi Bolivia

TECHNICAL DATA:

Dimensions:

60 × 60 × 100 cm HWD

Weight:

approx. 50 kg

Extent of Mechanization:

not mechanized

Form of Driving Energy:

only processing water and supplementary water

Mode of Operation:

continuous

Throughput/Capacity:

> 0.5 t/h

Technical Efficiency:

high separation precision

Operating Materials:

Type:

water

ECONOMIC DATA:

Investment Costs:

3-chamber, cif La Paz: 9000 US$; Taller Metal Mecanico Potosi: 500 DM

Operating Costs:

very low, low labor costs

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Personnel Requirements:

operating experience necessary

Location Requirements:

water and vertical gradient required

Grain Size:

< 1 mm

Output:

separates, according to equal-settling velocities, into 3 fractions plus fines-overflow

Replaces other Equipment:

screen classification, cone classifiers (settling boxes)

Regional Distribution:

worldwide

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under What Conditions:

qualified carpentry or metal workshop, high-quality screens must be available on the national market

Lifespan:

very long |————|————| very short

Bibliography, Source: Priester, Quittkat, Schubert, EP 0012740

OPERATING PRINCIPLE:

The countercurrent hydraulic classifier separates the feed into three or more fractions plus a fines-overflow by means of a cassifying chamber with partitioning walls of varying height. For each fraction to be separated, a bottom screen is provided through which an added underwater flow builds a fluidized bed or turbulent layer. Classified products are removed from the fluidized bed through pipe drains, located in the center of the bed and regulated by cone-shaped valves. In the direction of slurry flow, continually finer products, or products with increasingly slower settling velocities, are separated out. The process is regulated by both the added underwater current and the adjustable valves.

AREAS OF APPLICATION:

Classification of fine-grained feed into several fractions in a continuous operation.

REMARKS:

The precision of separation is higher than with cone classifiers (settling boxes). Extensive experience is required to optimally regulate the process in correlation with the particular feed material. The processing of sulfide ores requires that the equipment be of high-quality materials, especially the screens, since the processing waters are usually acidic and lead to extremely rapid corrosion.

The latest patent literature refers to a cross-current hydro-classifier serving as the basis for an analytical apparatus for examining the grain-size distribution in cement. This classifier has a very narrow and high cross-section, a small classifying-chamber volume, and comparably low throughput, but can continuously or semi-continuously separate the feed material into as many as seven fractions. This operating principle could be applied to hydraulic chamber classifiers for use in ore beneficiation as well.

SUITABILITY FOR SMALL-SCALE MINING:

Countercurrent hydraulic classifiers are very suitable for use in small-scale mining beneficiation operations. Low Investment costs, suitability for local production, drive-less operating systems, and high throughput characteristize this apparatus. Sufficient experience in regulating the apparatus is a prerequisite for optimal utilization; when newly Introduced, its proper use can only be achieved through on-thejob-training (educational requirements).

Fig.: Construction design of a hydro-classifier, type Taller Metal Mecanico, potosi. Source: Priester.

Fig.: Chamber classifier: 1) slurry feed inlet, 2) underwater inlet, 3) sand outlet, 4) sludge overflow, 5) overflow weir, 6) cam shaft, 7) performed bottom. Source: Quittkat.

Fig.: Patented classifier for cement samples; longitudinal and cross-section (patent no. EP 0012740).

13.7 Hydro-cyclone

Mining General (Gold, Ore)
Beneficiation, Classification

germ.:

Hydrozyklon

span.:

hidrociclon

Manufacturer:

AKW, Schauenburg, Dorr-Oliver, Warman, Mozley, Eduardo, Met. Lacha, Voican, Eq. Ind. Astecnia, IAA, INCOMAQ, Buena Fortuna, COMESA, FAHENA, FIMA, MAGENSA

TECHNICAL DATA:

Dimensions:

single cyclones with 10 - 1000 mm 0

Weight:

starting at approx. 1 kg

Extent of Mechanization:

not mechanized when operated only by hydrostatic pressure from the slurry

Power:

pressure of slurry

Form of Driving Energy:

hydrostatic, higher pressures only with the use of a pump, 0.3 - 40 bar

Alternative Forms:

pump with electric or hydromechanic drive system

Mode of Operation:

continuous

Throughput/Capacity:

throughput of slurry up to > 100 t/h, 100 - 2000 g acceleration, throughput is f (nozzle diameter for influent and overflow, and influent pressure). Grain-size of separation between 5 and 2150 ym (maximum 500 ym)

Operating Materials:

Type:

water

ECONOMIC DATA:

Investment Costs:

< 1000 DM

Operating Costs:

low

Related Costs:

pipelines for pressurized water and possibly slurry pump

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Personnel Requirements:

low

Location Requirements:

water and elevation difference (Dh) must be available

Grain Size of Feed:

separation cut-off grain-size up to 500 ym

Special Feed Requirements:

the higher the grain-size to be separated, the larger the diameter of the cyclone has to be.

Output:

depending on type of hydraulic cyclone, more classifying (acute-angled cyclone) or more sorting (obtuse-angled cyclone) occurs.

Replaces other Equipment:

classifiers and sorters for fine fractions

Regional Distribution:

rare in Latin America, otherwise widely distributed

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under What Conditions:

metal manufacturing workshop, or workshop for special plastics used in low-pressure cyclones

Lifespan:

very long |————|————| very short

depends upon abrasiveness of the feed material

Bibliography, Source: AKW, Shoukry, Schubert

OPERATING PRINCIPLE:

The slurry feed flows into the cyclone under acceleration (due to hydrostatic pressure) through a tangential inlet-nozzle. Inside the cyclone, the whirling slurry-flow is divided into two currents - an outer sinking portion and an inner ascending portion - as a result of a damping effect from the cyclone's lower conical section. Under these conditions, the heavier or coarser grains comprise the descending slurry-flow and are removed with the underflow, whereas the finer-grained material enters the ascending slurry-flow and is carried out with the overflow (see sketches).

Hydro-cyclones are differentiated according to their areas of application:

- acute-angled hydro-cyclone: solid-fluid-separation (thickening, solids separation), cone angle 10° - 20°,
- intermediate design: classification (cone angle < 20°), - cylindrical hydro-cyclones: sorting, pre-concentration, etc. (CBC-cyclones).

AREAS OF APPLICATION:

- thickening of finest (silty) slurries, suspensions, etc. - desliming
- classification, for example in conjunction with carefully-controlled comminution involving preliminary and intermediary classifying in the milling process
- selective classification, such as for two materials of varying fineness (e.g. quartz sand, kaolin)
- sorting or classifying separation in order to pre-concentrate fine heavy-mineral fractions, e.g. gold, tin or tungsten ores.

SPECIAL AREAS OF APPLICATION:

Sink-and-float method in a heavy-medium cyclone with ferro-silicon.

In this process, separation occurs in a slurry of magnetite or ferrosilicon (FeSi) of a defined density. The dense material can be removed later by magnetic separation. Best results are achieved using atomized dense material due to the rounded grates and also the production process, which lead to:

- low viscosity of slurry
- greater resistance to corrosion
- lower mechanical abrasive wear of the powder
- lower mechanical abrasive wear of the machine
- lower surface adhesion of the beneficiated product

Slurry densities of between 2.0 and 3.8 kg/1 can be achieved with FeSi, enabling ores of iron, manganese, chromite, lead, tin and zinc, as well as fluorite, barite, diamonds, gravel and scrap-iron to be separated.

REMARKS:

A hydro-cyclone classification performed prior to separation with spiral separators, concentrating tables, settling basins, etc., whereby grains are sorted primarily according to their surface area exposed to flow forces, produces a more precise separation than with screen classification.

DESIGN CONSIDERATIONS:

The hydro-cyclone component most susceptible to wear is the underflow nozzle, which is subjects to coarse grains flowing through at relatively high pressure. Various designs for underflow nozzles exist which can extend the lifespan of a cyclone:

- hard-porcelain lining
- replaceable underflow nozzle made of wear-resistant material (rubber, PU, hard
porcelain)
- pneumatically-controlled rubber discharge nozzle - manually-controlled rubber discharge nozzle

For normal acute-angled cylindrical-conical cyclones with intake angles of 10°- 20°, the following dimensions can be recommended:

D_i = (0.15 - 0.25) Dc where

D_c : diameter of cyclone

D_o = (0 20 - 0-40) Dc where

D_i : diameter of intake nozzle

D_a = (0.15 - 0.80) Do where

D_o : diameter of overflow nozzle

D_a : diameter of underflow nozzle

The finer the separaion cut-off grain size, the smaller the diameter of the cyclone and the higher the intake pressure must be.

SUITABILITY FOR SMALL-SCALE MINING:

Due to the diverse areas of application for purposes of desliming or desilting, classifying or sorting, the hydro-cyclone is very suitable for small-scale mining. Prerequisite for drive-less operation is the minimal elevation gradient of 3 - 10 m. Even considering that hydro-cyclones can only be locally produced in exceptional cases, they are still appropriate particularly for sorting classification purposes. Hydro-cyclones are comparably simple in design and low in cost.

Fig.: Diagram of flow pattern in a hydro-cyclone. Source: AKW.

Fig.: Various types of cyclones for desliming (left, classifying (middle) and sorting (right). Source: AKW.

Figures
Fig.: Pneumatically-controlled under-flow nozzle for hydro-cyclones, made of elasomer. Source: Guelt

Fig.: Modular construction of a hydro-cyclone. Source: Shoukry.

13.8 Log washer, spiral classifier

Mining General
Benefication, Classification

germ.:

Logwasher, Spiralklassierer

span.:

atrisionador, clasificador de espiral

Manufacturers of spiral classifiers:

FUNSA, Volcan, IAA, COMESA, FAHENA, FIMA, Famia, Fund. Callao, MAGENSA, MAEPSA, Met. Mec. Soriano, PROPER, FAMESA

TECHNICAL DATA:

Dimensions:

1 × 1 × 8 m HWD, inclination 1: 20, shaft diameter 18", length of shovel 9", also smaller dimensions possible

Weight:

several tons

Extent of Mechanization:

semi-mechanized

Power:

up to 25 PS, double-classifier up to 30 PS, 15 - 20 min-1

Form of Driving Energy:

belt transmission from internal combustion engine, electric motor

Alternative Forms:

turbine/water wheel

Mode of Operation:

semi-continuous

Throughput/Capacity:

up to 100 t/24 h

Operating Materials:

Type:

water

Quantity:

up to 200 I/min

ECONOMIC DATA:

Investment Costs:

when locally produced 1000 to 5000 DM

Operating Costs:

depends on drive system

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Location Requirements:

water requirements must be met

Grain Size of Feed:

< 5 - 10 cm

Output:

cclassified into underflow (silt and fine fraction) and overflow (coarse fraction)

Replaces other Equipment:

sppiral classifier

Regional Distribution:

USA, Australia

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

if hard lumber is available

Under What Conditions:

wood and metal-manufacturing workshops

Lifespan:

very long |————|————| very short

Bibliography, Source: v. Bernewitz, Schennen

OPERATING PRINCIPLE:

Analogous to spiral classifiers. The slurry, fed onto the lower one-third of the shaft, is separated by means of the shovels into an upward-flow containing the coarse, heavy grains and a downward-flow containing the light-weight grains. The classification box of rectangular cross-section fills with material at the start of the process before the actual classification begins.

AREAS OF APPLICATION:

Desliming, classification, drainage, and separating of the ground product in grinding circuits.

REMARKS:

Construction does not require that the housing be adjusted to the cross-section of the shaft since gaps are filled with minerals.

Separation cut-off grade is determined by angle of inclination.

SUITABILITY FOR SMALL SCALE MINING:

In smaller dimensions log washers are also appropriate for small-scale mining classification purposes if a suitable drive-system is available at low energy costs. Log washers are very suitable for local production.

Fig.: Schematic diagram of a log washer. Source: Bernewitz.

Fig.: Design of a single spiral classifier: 1) motor, 2) drive, 3) gear wheel, 4) spiral, 5) lifting device, 6) outlet, 7) feed intake, 8) flow (transport) direction, 9) discharge, 10) traverse. Source: Schiedchen.

13.9 Rake classifier

Deep Mining General
Beneficiation, Classification

germ.:

Rechenklassierer

span.:

clasificador transportador a rastrillo

Manufacturer:

Volcan, Eq. Ind. Astecnia, IAA, COMESA, FAHENA, MAENSA, FAMESA

TECHNICAL DATA:

Dimensions:

1.2 × 3.5 × 1.0 m HWD for a small rake classifier, working frequency 10 - 30 min-1, minimum angle of inclination 12 Weight: approx. 600 kg

Extent of Mechanization:

ully mechanized

Power:

1.5 PS

Form of Driving Energy:

mechanical via electric motor, internal combustion engine, turbine

Mode of Operation:

continuous

Throughput/Capacity:

0.5-1 t/h

Operating Materials:

Type:

water

ECONOMIC DATA:

Investment Costs:

minimum of 10.000 DM when locally produced

Operating Costs:

low, primarily energy costs

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————|high

Location Requirements:

none, except water

Grain Size of Feed:

high proportion of fine grains (0.1 - 0.5 mm) necessary to guarantee stability of the suspension. Only under these conditions can a rake classifier separate with high precision.

Special Feed Requirements:

30 - 50 % by vol. solids in the slurry

Output:

the classifying is regulated by controlling the slurry density

Replaces other Equipment:

spiral classifier

Regional Distribution:

very rare

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

Suitability for Local Production:

very good |————|————| bad

Under What Conditions:

national machinery manufacturers

Lifespan:

very long |————|————| very short

Bibliography, Source: Gerth

OPERATING PRINCIPLE:

In a declined trough, the coarse material is scraped upwards by a rake. At the return point, the rake is lifted, moved back down to the initial position and lowered onto the bottom of the trough. The fine material remains suspended and flows out over a weir at the lower end of the trough. The slurry-feed intake is located about a third of the way up from the lower end of the trough.

AREAS OF APPLICATION:

For intermediary classification of milled material in a closed grinding circuit.

REMARKS:

Very low wear, limited to the rake.

The rake has a very long lifespan due to the possibility to adjust its height. For lead-zinc ore, Gerth estimates a rake lifespan of approx. 30.000 t throughput (rake height worn from 60 down to 20 mm).

SUITABILITY FOR SMALL-SCALE MINING:

Rake classifiers are characterized by their simple construction and low wear' and are suitable for small scale mining if they can be nationally manufactured.

Fig.: Schematic diagram of a rake classifier. Source: Schmiedchen.

Fig.: Simplified elevation drawing of a rake classifier. Source: Schmiedchen.

13.10 Sluice, sluice box, washing sluice

Mining General
Beneficiation, Classification

germ.:

Lauterrinne, Ablauterrinne, Waschrinne

span.:

canaleta de lavado, canaleta de relavado, canaleta de limpieza .

TECHNICAL DATA:

Dimensions:

inclination: approx. 10°, several stepped sections approx. 50 - 60 cm in width and 50 cm in depth, 4 - 5 m total length

Weight:

masonry construction, built into the ground

Extent of Mechanization:

not mechanized

Form of Driving Energy:

uses the energy of flowing water, possibly supported by turning the material with rakes, shovels, etc.

Throughput/Capacity:

several tons of material per hour

Operating Materials:

Type:

water

Quantity:

at least ten times the feed quantity

ECONOMIC DATA:

Investment Costs:

very low since the sluice is built into the ground with minimal effort

Operating Costs:

labor costs only

Related Costs:

beneficiation equipment for the fine slurry, e.g. settling basins or buddies

CONDITIONS OF APPLICATION:

Operating Expenditures:

low |————|————| high

Maintenance Expenditures:

low |————|————| high

Location Requirements:

water must be available in large quantities

Grain Size of Feed:

from silt fraction (fines) to approx. 200 mm

Special Feed Requirements:

washing (i.e. dissociation of strongly baked, partially solidified grain bonds) must occur during beneficiation of conglomerates and breccia, or during re-processing of old waste deposits or abandoned workings

Output:

coarse fraction is sufficiently cleaned to allow hand-sorting

Replaces other Equipment:

washing drum, autogenous mill

Regional Distribution:

found rarely in small-scale mining, e.g. in Bolivia/Potosi

Operating Experience:

very good |————|————| bad

Environmental Impact:

low |————|————| very high

depending on type of feed, sludge (fines) loading can occur, requiring a subsequent fines separation, when necessary with sludge pond or settling basin.

Suitability for Local Production:

very good |————|————| bad

Under What Conditions:

local production is easily possible since only simple masonry work is involved

Lifespan:

very long |————|————| very short

Bibliography, Source: Rittinger

OPERATING PRINCIPLE:

The feed material in the washing sluice is separated into its individual components through the energy conveyed by the flowing water and through supplementary agitation (manually-operated shovels, rakes, etc.).

AREAS OF APPLICATION:

For crushing and classifying slightly-solidified conglomerates and breccia as well as cemented crude ore from underground mines, old deposits or abandoned workings.

REMARKS:

To process feed with high clay content, e.g. from abandoned works, the material is mixed with water in a basin or pit and is repeatedly kneaded by means of stamping or worked with scrapers or picks. In this way, the adhesive and cohesive forces of the cemented clay fractions are broken down. This process is called ch'etachado in Quechua. It is very work intensive, but in combination with subsequent washing in a sluice, it is the only possibility for non-mechanized mines to process feeds with high clay contents.

SUITABILITY FOR SMALL-SCALE MINING:

Washing in sluices is the simplest method of crushing and classifying slightly-solidified feed or feed materials of high clay content.

engl.:	screening gate, grizzly
germ.:	Siebklassierung in starren Sieben, Durchwurf, Reibgatter
span.:	clasificacion en tamices fijos, clasificacion por tamano en tamiz

TECHNICAL DATA:
Dimensions:	starting at 30 × 40 cm screen area for single screen, up to 2 × 2 m for coarse screens (grizzly)
Weight:	starting at 5 kg per screen
Extent of Mechanization:	not mechanized
Form of Driving Energy:	manual feeding, possible manual drawing as well
Mode of Operation:	semi-continuous
Throughput/Capacity:	very dependent on grain-size of feed
Operating Materials:
Type:	water for wet screening
ECONOMIC DATA:
Investment Costs:	example: for three screens 300 DM
Operating Costs:	labor costs only

Operating Expenditures:	low \|————\|————\| high
Maintenance Expenditures:	low \|————\|————\| high
Location Requirements:	water availability
Grain Size:	100 ym up to several decimeters separation cut-off size (screen openings)
Special Feed Characteristics:	no clay-containing' sticky material
Replaces other Equipment:	other classifiers
Regional Distribution:	worldwide
Operating Experience:	very good \|————\|————\|bad
Environmental Impact:	low \|————\|————\|very high
Suitability for Local Production:	very good \|———\|————\|bad
Under What Conditions:	frames are very suitable for local production by carpentry or metal workshops; screens are generally imported since they are subject to extreme abrasive forces and must therefore be constructed of high-quality material.
Lifespan:	very long \|————\|————\| very short

germ.:	Ruttelsiebe, Schwingsiebe, Ratter
span.:	criba vibradora, instalacion de tamices con movimiento circular
Manufacturer:	Schenk, Jost, Mogensen, Eduardo, INCOMEC, Milag, Met. Cancha, Volcan, Alquexco, Eq. Ind. Astecnia, IAA, INCOMAQ, COMESA, FAHENA, Telsmith, FIMA, FAMINCO, Famia, fund. Callao, H.M., MAGENSA, MAENSA, MAEPSA, Met. Callao E.P.S.

TECHNICAL DATA:
Dimensions:	from 30 × 40 cm upwards, 10° - 20° inclination, 80 - 100 min-1 vibrating or shaking frequency
Weight:	from approx. 50 kg up to several thousand kg
Extent of Mechanization:	fully mechanized
Power:	low, maximal 1 PS/m² screen area
Form of Driving Energy:	hydromechanic impact mechanisms, manual impact mechanisms
Alternative forms:	pedal drive
Mode of Operation:	continuous
Technical Efficiency:	comparably higher than that of rigid screens
Operating Materials:
Type:	water
Quantity:	60 - 80 % by volume of feed quantity
ECONOMIC DATA:
Investment Costs:	manual, starting at 100 DM per screen when locally produced
Operating Costs:	usually labor costs only, possibly energy costs
Related Costs:	drive system

Operating Expenditures:	low \|————————\| high
	depending upon degree of mechanization
Maintenance Expenditures:	low \|————\|————\| high
	the removal of adhesive (sticky) grains in the feed is necessary
Location Requirements:	water availability
Grain Size:	> 50,um up to < 50 mm
Replaces other Equipment:	rigid screens
Regional Distribution:	not known in semi-mechanized processes in small-scale mining in Latin America; only used for wet classification in Jig operations
Operating Experience:	very good \|————\|————\| bad
Environmental Impact:	low \|————\|————\| very high
Suitability for Local Production:	very good \|————\|————\| bad
Under What Conditions:	wood and metal manufacturing shops
Lifespan:	very long \|————\|————\| very short

germ.:	Antriebslose Schwingsiebe
span.:	criba vibradora sin fuerza motriz (parrilla)
Manufacturer:	Mogensen

TECHNICAL DATA:
Dimensions:	separable grain-size cut-off: 25 - 40 mm minimum, approx. 300 mm maximum
Weight:	from approx. 200 kg
Extent of Mechanization:	not mechanized
Form of Driving Energy:	uses impact of falling feed material to induce shaking
Alternative forms:	as vibro-sizer for material that is very difficult to screen, but then mechanized
Mode of Operation:	continuous
Throughput/Capacity:	> 100 t/h
ECONOMIC DATA:
Investment Costs:	minimum of 20.000 DM fob location of manufacture in Germany
Operating Costs:	very low

germ.:	Klassiertrommel
span.:	tromel clasificador, criba rotativa
Manufacturer:	Milag, Met. Lacha, Alquexco, IAA, Buena Fortuna, FAHENA, FIMA, MAGENSA, MAEPSA, Met. Callao E.P.S.

TECHNICAL DATA:
Dimensions:	18 - 25 min-1 rpm, circumferential speed < 1 m/s, diameter 2 0.5 m, length 2 m for single drum with three sizing grades
Weight:	starting at approx. 100 kg for smaller types
Extent of Mechanization:	semi-mechanized
Driving Capacity:	starting at 0.5 kW
Form of Driving Energy:	hydromechanic
Alternative Forms:	internal combustion engine, electric drive, manual operation for small models
Mode of Operation:	continuous
Throughput/Capacity:	minimum 1 t/h;
	for dry screening:	0.27 t/m²h per mm screen opening
	for wet screening:	0.45 t/m²h per mm screen opening
Operating Materials:
Type:	water
ECONOMIC DATA:
Investment Costs:	starting at approx. 1500 DM
Operating Costs:	mainly energy costs

engl.:	box classifier, settling box
germ.:	Spitzkasten
span.:	clasificador de caja en punta, caja en punta
Manufacturer:	FIMA

TECHNICAL DATA:
Dimensions:	from about 1 × 0.8 × 2 m up to several m in width and over 10 m in length
Weight:	from approx. 40 kg
Extent of Mechanization:	not mechanized
Form of Driving Energy:	only processing-water current
Mode of Operation:	continuous
Operating Materials:
Type:	water
Quantity:	slurry with < 40 % by vol. solids
ECONOMIC DATA:
Investment Costs:	approx. 200 DM when locally produced
Operating Costs:	labor costs only

No.	width	length	� discharged material
1	1 m	2 m	40 % of the weight
2	2 m	3 m	20 % of the weight
3	3 m	4 m	18 % of the weight
4	4 m	5 m	10 % of the weight

engl.:	chamber classifier
germ.:	Aufstrom-Hydroklassierer, Kammerklassierer
span.:	hidroclasificador de corriente ascendente, clasificador hidraulico, clasificador de cameras
Manufacturer:	Denver Peru, TMM Potosi Bolivia

TECHNICAL DATA:
Dimensions:	60 × 60 × 100 cm HWD
Weight:	approx. 50 kg
Extent of Mechanization:	not mechanized
Form of Driving Energy:	only processing water and supplementary water
Mode of Operation:	continuous
Throughput/Capacity:	> 0.5 t/h
Technical Efficiency:	high separation precision
Operating Materials:
Type:	water
ECONOMIC DATA:
Investment Costs:	3-chamber, cif La Paz: 9000 US$; Taller Metal Mecanico Potosi: 500 DM
Operating Costs:	very low, low labor costs

germ.:	Hydrozyklon
span.:	hidrociclon
Manufacturer:	AKW, Schauenburg, Dorr-Oliver, Warman, Mozley, Eduardo, Met. Lacha, Voican, Eq. Ind. Astecnia, IAA, INCOMAQ, Buena Fortuna, COMESA, FAHENA, FIMA, MAGENSA

TECHNICAL DATA:
Dimensions:	single cyclones with 10 - 1000 mm 0
Weight:	starting at approx. 1 kg
Extent of Mechanization:	not mechanized when operated only by hydrostatic pressure from the slurry
Power:	pressure of slurry
Form of Driving Energy:	hydrostatic, higher pressures only with the use of a pump, 0.3 - 40 bar
Alternative Forms:	pump with electric or hydromechanic drive system
Mode of Operation:	continuous
Throughput/Capacity:	throughput of slurry up to > 100 t/h, 100 - 2000 g acceleration, throughput is f (nozzle diameter for influent and overflow, and influent pressure). Grain-size of separation between 5 and 2150 ym (maximum 500 ym)
Operating Materials:
Type:	water
ECONOMIC DATA:
Investment Costs:	< 1000 DM
Operating Costs:	low
Related Costs:	pipelines for pressurized water and possibly slurry pump

D_i = (0.15 - 0.25) Dc where	D_c : diameter of cyclone
D_o = (0 20 - 0-40) Dc where	D_i : diameter of intake nozzle
D_a = (0.15 - 0.80) Do where	D_o : diameter of overflow nozzle
	D_a : diameter of underflow nozzle

germ.:	Logwasher, Spiralklassierer
span.:	atrisionador, clasificador de espiral
Manufacturers of spiral classifiers:	FUNSA, Volcan, IAA, COMESA, FAHENA, FIMA, Famia, Fund. Callao, MAGENSA, MAEPSA, Met. Mec. Soriano, PROPER, FAMESA

TECHNICAL DATA:
Dimensions:	1 × 1 × 8 m HWD, inclination 1: 20, shaft diameter 18", length of shovel 9", also smaller dimensions possible
Weight:	several tons
Extent of Mechanization:	semi-mechanized
Power:	up to 25 PS, double-classifier up to 30 PS, 15 - 20 min-1
Form of Driving Energy:	belt transmission from internal combustion engine, electric motor
Alternative Forms:	turbine/water wheel
Mode of Operation:	semi-continuous
Throughput/Capacity:	up to 100 t/24 h
Operating Materials:
Type:	water
Quantity:	up to 200 I/min
ECONOMIC DATA:
Investment Costs:	when locally produced 1000 to 5000 DM
Operating Costs:	depends on drive system

germ.:	Rechenklassierer
span.:	clasificador transportador a rastrillo
Manufacturer:	Volcan, Eq. Ind. Astecnia, IAA, COMESA, FAHENA, MAENSA, FAMESA

TECHNICAL DATA:
Dimensions:	1.2 × 3.5 × 1.0 m HWD for a small rake classifier, working frequency 10 - 30 min-1, minimum angle of inclination 12 Weight: approx. 600 kg
Extent of Mechanization:	ully mechanized
Power:	1.5 PS
Form of Driving Energy:	mechanical via electric motor, internal combustion engine, turbine
Mode of Operation:	continuous
Throughput/Capacity:	0.5-1 t/h
Operating Materials:
Type:	water
ECONOMIC DATA:
Investment Costs:	minimum of 10.000 DM when locally produced
Operating Costs:	low, primarily energy costs

germ.:	Lauterrinne, Ablauterrinne, Waschrinne
span.:	canaleta de lavado, canaleta de relavado, canaleta de limpieza .

TECHNICAL DATA:
Dimensions:	inclination: approx. 10°, several stepped sections approx. 50 - 60 cm in width and 50 cm in depth, 4 - 5 m total length
Weight:	masonry construction, built into the ground
Extent of Mechanization:	not mechanized
Form of Driving Energy:	uses the energy of flowing water, possibly supported by turning the material with rakes, shovels, etc.
Throughput/Capacity:	several tons of material per hour
Operating Materials:
Type:	water
Quantity:	at least ten times the feed quantity
ECONOMIC DATA:
Investment Costs:	very low since the sluice is built into the ground with minimal effort
Operating Costs:	labor costs only
Related Costs:	beneficiation equipment for the fine slurry, e.g. settling basins or buddies