COAL AND METALS CASES

CASES——Coal

After the coal is mined and sized,it is ground with a ball mill and then separated by gravity from the waste residue in an aqueous medium.Coal floats and waste sinks.The coal is then re-sized and sep-arated into finished products.

In this process,fine coal particles will be generated and suspended in the water.In order to recycle water resources and recover fine coal particles,the separa-tion of coal particles and water is usually promoted by flotation.Flocculants are used in the flotation process to promote solid-liquid separation.

Clean water is generated from the overflow of thickener and recycled back to the preparation plant,so as to continue to use in subsequent flushing flotation and recover fine coal products through filtration or centrifugation.

When dealing with lignite or coal with high clay con-tent,it is sometimes necessary to use coagulant before adding flocculant in order to achieve effective solid capture and accept-able overflow clarity.

CASES——Copper

Copper processing,the extraction of copper from its ores and the preparation of copper metal or chemical compounds for use in various products.In the ore-dressing plant,the material received from the mine is crushed in several stages and finely ground to a size which ensures that copper minerals are liberated from the waste materials,or gangue.

In cases where the next step is leaching (most frequently in the case of oxide ores),complete liberation of the copper minerals is not always necessary: the ore needs to be crushed and ground only to the extent required to expose the surface of the minerals to the leaching agent.For sulfide ores,on the other hand,selective flotation normally follows the crushing and grinding stage and requires an optimal degree of liberation.

In the flotation process,the finely ground ore,mixed with water and special reagents,is agitated by mechanical and pneumatic devices.These produce air bubbles in the ore-water mixture,or slurry.The reagents provide an attraction between the surface of the copper minerals and the air bubbles and the flocculant is widely used in the concentrator and tailing disposal processes.As the bubbles rise to the surface,they carry the copper minerals with them,leaving gangue minerals in the cell to be discarded as tailings.Collection of the froth from the surface of the flotation cell froth(containing yields a copper concentrate.To increase the recovery of copper and reduce losses,the tailings are frequently reground and passed through a second flotation,the conadhering to centrate from which is combined bubbles with the initial production.The flotation concentrate is then dewatered containing and filtered to produce a filter cake agitator nydrophilic matenal) that is sent to a copper smelter.

CASES——Gold/Silver

Most gold and silver processes today extract the mineral by use of either Carbon in Pulp (CIP)or Carbon in Leach (CIL)processes.Here activated carbon is used to recover gold,which has been dissolved by the addition of cyanide.

Prior to leaching the ores crushed and screened then passed to ball mills where water and lime is added.The solids are then settled in a preleaching thickener with the addition of a flocculant to promote rapid settlement and good compaction.The underflow is then subjected to the leaching process via a series of leaching tanks.The tanks allow sufficient retention time for the gold and silver to be dissolved by the cyanide process.

The slurry then moves to a series of carbon adsorption tanks where the gold and silver are removed from solution.This is done by feeding carbon through the tanks,in the opposite direction of the slurry flow,with the gold/silver then adsorbing of the carbon granules.

By the time the slurry has reached the final adsorption tank most of the precious metals have been removed.The barren slurry,or tailing.is then pumped to the tailing lagoons.By the time the carbon reaches the first adsorption tank it has recovered most of the gold and silver from solution.This loaded carbon is then pumped to the elution circuit where the gold and silver are washed off with superheated water.The washed solution is passed to the electro-winning circuit for metals recovery.