Spiral mineral processing

Spiral Concentration Principle

Spiral concentrators utilize the inclined flow on a spiral trough surface for mineral separation. The spiral trough surface is inclined both longitudinally and laterally (radially). Mineral particles located on the spiral trough surface move under the combined action of fluid dynamics, gravity, inertial centrifugal force, and friction at the trough bottom, undergoing stratification and zoning during this movement. Within the material layer, mineral particles stratify due to differences in gravitational pressure; heavier particles enter the bottom layer, lighter particles move to the upper layer, and a mixed layer exists in between. After initial stratification, the material, under the influence of the spiral flow and the lateral (radial) circulation, moves downwards along the vertical centerline of the trough while simultaneously zoning along the trough width. Mineral particles in the upper layer gradually move towards the outer edge due to the outward flow of the lateral circulation layer, while those in the lower layer gradually move towards the inner edge due to the inward circulation at the bottom and the component of gravity. During stratification and zoning, due to the separation stratification effect, finer, heavier mineral particles settle to the bottom layer. Ultimately, heavy mineral particles are distributed along the inner edge, with fine heavy mineral particles distributed along the innermost edge; light mineral particles are distributed along the outer edge, with coarse light mineral particles distributed along the inner side of the outer edge and fine light mineral particles distributed along the outermost edge. Different products can be obtained by collecting the separated material using a separator or separating plate. Adjusting the position of the separator or separating plate can adjust the product yield and grade.

Spiral concentrators are used to process ores ranging from 3 to 0.02 mm in size. The concentrator process is continuous, with separation efficiency similar to shaking tables. The equipment has a simple structure, is easy to operate, and has a large processing capacity.

Spiral concentrator equipment includes three types: spiral concentrators, spiral sluices, and rotary spiral sluices.

2.6.2 Spiral Concentrator Equipment

2.6.2.1 Spiral Concentrator

Its structure is shown in Figure 2-38. It was successfully developed by J.B. Humphreys of the United States in 1941. Over the next half-century, it underwent continuous improvements in cross-sectional shape, feed trough, discharge trough, flushing water trough, and manufacturing materials, and has developed towards multi-head (multi-layer) designs.

The spiral concentrator’s spiral separating trough is installed vertically, and its cross-section approximates a quadratic parabola or a quarter ellipse. The spiral separating trough is the main separating component, and its cross-sectional shape, diameter, and pitch are the main structural parameters affecting the separating performance. The main process parameters of the spiral concentrator are slurry flow rate, slurry concentration, ore particle size, and supplementary flushing water.

Figure 2-38 Spiral Concentrator

1 — Feed trough;

2 — Flushing water guide trough;

3 — Spiral trough;

4 — Connecting flange;

5 — Tailings trough;

6 — Frame;

7 — Heavy mineral discharge pipe

It is mainly used for separating ores containing tungsten, tin, iron, tantalum, niobium, etc., with a diameter of 3-0.05 mm, as well as placer deposits containing ilmenite, rutile, zircon, monazite, gold, and platinum. During operation, the feed rate and slurry concentration must be stable, and weeds, sawdust, and other impurities must be removed beforehand.

2.6.2.2 Spiral Conveyor The spiral sluice is a vertically installed spiral-shaped sorting trough. Its cross-sectional shape is a cubic parabola, wider than that of a spiral concentrator, providing a wider, gentler area with a thinner slurry layer and lower flow velocity, which is beneficial for separating fine-grained ores. Compared to a spiral concentrator, its operation differs in that it does not use flushing water; the product is collected at the end of the sluice, not through an opening in the middle. It is mainly used for separating iron, tungsten, tin, and titanium ores of 0.2~0.02 mm and for processing placer deposits containing ilmenite, rutile, zircon, monazite, and gold.

Figure 2-39 Rotary Spiral Chute

1—Water hopper; 2—Ore hopper; 3—Spiral chute;

4—Vertical shaft; 5—Frame; 6—Washing water tank;

7—Cutter; 8—Receiving trough; 9—Pulley;

10—Speed-regulating motor; 11—Concentrate trough; 12—Mid-ore trough; 13—Tailles trough

2.6.2.3 – Rotary Spiral Sluice Box

Its structure is shown in Figure 2-39. It was successfully developed by the Xinjiang Metallurgical Research Institute in my country in 1977. The spiral sorting sluice box is vertically installed and rotates around a vertical axis in the direction of slurry flow. Its specifications are a diameter of 936 mm and a rotation speed of 10-15 rpm. The sluice box surface is equipped with raised bars or grooves. The raised bars are 6-0 mm high and 6 mm wide, and the spiral groove is 400 mm wide. It achieves good results in sorting tantalum-niobium slime of 0.8-0.076 mm, with enrichment ratios reaching 45-75, far exceeding that of ordinary spiral sluice boxes. However, its effective recovery particle size limit is relatively coarse, making it unsuitable for recovering fine-grained ores.