Effect of Operating Variables on Metallurgical Process

VARIABLE	RANGE	EFFECT ON PROCESS
Crushing
Jaw Crusher Close side setting	3″ plus	H – Material too large for cone crusher.
		N – 3″
		L – Reduction in capacity. Excess power draw.
Cone Crusher Close side setting	3/8″ – 1″	H – Increased circulating load of screen and cone.
		N – 1/2″
		L – Increased power consumption, decrease capacity.
Dust Collector recirculating % solids	7 – 10%	H– Excessive nozzle and impeller wear.
		N – 8%
		L – No effect.
Grinding
Mill Feed Conveyor Speed (feed rate)	0-33 mtph	H– May overload mill with increase in circulating load.
		N – 22 mtph
		L – Decrease in plant throughput.
Mill Percent solids	50-70%	H-Increase in circulating load. Poor grinding efficiency.
		N – 60%
		L – Increase throughput but decreases grinding efficiency
Cyclone Feed Density	45 – 60%	H– Coarse particles in cyclone overflow.
		N – 52% solids.
		L – Fine particles in cyclone overflow, less product.
Cyclone 0/F density	25 – 35%	H– Coarse particle in cyclone overflow, potential to sand gravity line to thickener.
		N – 30%
		L – Fine particles in cyclone overflow.
Cyclone Apex opening	2 “-4”	H – Decrease cyclone underflow density.
		N – As required.
		L – Increase cyclone underflow density and potential ‘roping’ condition.
Cyclone 0/F pH	10-11	H – Waste of lime.
		N – 10.5
		L – Danger of HCN generation.
Cyclone U/F density	60-75%	H – Coarse particles in cyclone overflow and increase in circulating load.
		N – 69%
		L – Fine particles in cyclone underflow, less product.
Thickening
Thickener Overflow clarity	15-100 ppm	H – Increase load on clarifier
		N – 50 ppm.
		L – Good.
Thickener Underflow solids	50-70%	H – Potential for sanding lines.
		N – 60%
		L – Excess pregnant solution in leach feed.
Thickener Flocculant addition	25-100 gm/t	H – Waste of flocculant and underflow could become jelly-like.
		N – 50 gm/tonne.
		L – Solids increase in thickener overflow.
Leaching
Leaching Cyanide concentration	5-9 kg/tonne	H – Waste of cyanide, may dissolve undesirable metals.
		N – 7 kg/tonne
		L – Incomplete precious metals dissolution.
Leaching Air addition	2-3 kg/tonne	H – Wasting lime.
		N – 2.55 kg/tonne
		L – HCN generation, incomplete precious metals dissolution.
Leaching Pulp density	40-50%	H – Excess power required to keep slurry in suspension, solids may scale.
		N – 45%
		L – Decrease in retention time, hence recovery.
Filtration
Filtration Filter feed pH	11.5-12.5	H – Waste of lime.
		N – 12.0
		L – Poor filtration, slimly cake and reduced throughput.
Filtration Vacuum	18-25″ Hg	H – Wasting energy.
		N – 22″ Hg
		L – Increase in cake moisture, poor pregnant solution recovery, slimly cake.
Filtration Flocculant addition	50-100 gm/tonne	H – Waste of flocculant.
		N – 75 gm/tonne
		L – Blinding of filter cloth.
Flotation
Flotation Air		H – Will float waste (gange) material.
		N – 100/30 S C F M rougher/cleaner cells.
		L – Poor froth generation and recovery.
Merrill-Crowe
Deaeration Vacuum	18-25″ Hg	H – Waste of energy.
		N – 22″ Hg
		L – Poor removal of oxygen from solution, gold/silver will redissolve.