Copper ore leaching processing

The above flowsheet shows a basic copper mine process, from mine to metal. There are two distinct types of copper ore, the sulfide ore and the oxide ore. The sulfide ores are beneficiated in flotation cells, while the oxide ores are generally leached. First the copper ore from a open pit mine is blasted, loaded and transported to the primary crushers. Then the ore is crushed and screened, with the fine sulfide ore (~-0.5 mm) going to froth flotation cells for recovery of copper. The coarser ore goes to the heap leach, where the copper is subjected to a dilute sulfuric acid solution to dissolve the copper. Then the leach solution containing the dissolved copper is subjected to a process called solvent extraction (SX). The SX process concentrates and purifies the copper leach solution so the copper can be recovered at a high electrical current efficiency by the electrowinning cells. It does this by adding a chemical reagent to the SX tanks which selectively binds with and extracts the copper, is easily separated from the copper (stripped), recovering as much of the reagent as possible for re-use. The concentrated copper solution is dissolved in sulfuric acid and sent to the electrolytic cells for recovery as copper plates (cathodes). From the copper cathodes, it is manufactured into wire, appliances, etc. that are used in every day life. Below are some photos of the process equipment at an Arizona Copper Mine.

Copper Ore being loaded into a 300 ton truck for transport to the crusher

The primary crusher at a copper mine. The truck dumps ore into the crusher which crushes the ore. Screens size and distribute the classified ore to a series of conveyors, like those above, for transportation to the mill for further processing.

Conveyors and trucks deposit coarse ore on a heap leach pad, which has a series of pipes and hoses dispensing a diluted sulfuric acid solution to the ore. Copper is dissolved and flows to a pond at the bottom of the pad. This process can take several months. The leached solution is pumped to the SX (Solvent Extraction) circuit, which looks like a series of agitation tanks or cells. The fine sulfide ore is sent to froth flotation cells like those below for recovery.

The froth flotation cells recover the copper from sulfide ores by chemically attaching the copper to a chemical bubble and overflowing the froth (bubbles with copper).

The concentrates from the flotation cells are sent to the smelter for processing to a copper plate. The copper plate is then dissolved in sulfuric acid and sent to the electrowinning cells for plating onto cathodes, along with the concentrated copper from the SX circuits. The copper leach solution typically consists of 40 gm of copper and 200 gm sulfuric acid per liter. Current densities on the electrowinning cells can be 300 amperes per square foot, or more.

Gold and Copper Processing Methods

Gold is extracted from naturally-oxidized ores by either heap leaching or milling, depending on the amount of gold contained in the ore, the amenability of the ore to treatment and related capital and operating costs. Higher grade oxide ores are generally processed through mills, where the ore is ground into a fine powder and mixed with water in slurry, which then passes through a carbon-in-leach circuit. Lower grade oxide ores are generally processed using heap leaching. Heap leaching consists of stacking crushed or run-of-mine ore on impermeable pads, where a weak cyanide solution is applied to the surface of the heap to dissolve the gold. In both cases, the gold-bearing solution is then collected and pumped to process facilities to remove the gold by collection on carbon or by zinc precipitation.

Gold contained in ores that are not naturally oxidized can be directly milled if the gold is amenable to cyanidation, generally known as free milling sulfide ores. Ores that are not amenable to cyanidation, known as refractory ores, require more costly and complex processing techniques than oxide or free milling ore. Higher-grade refractory ores are processed through either roasters or autoclaves. Roasters heat finely ground ore to a high temperature, burn off the carbon and oxidize the sulfide minerals that prevent efficient leaching. Autoclaves use heat, oxygen and pressure to oxidize sulfide ores.

Some sulfide ores may be processed through a flotation plant or by bio-milling. In flotation, ore is finely ground, turned into slurry, then placed in a tank known as a flotation cell. Chemicals are added to the slurry causing the gold-containing sulfides to float attached to air bubbles to the top of the tank. The sulfides are removed from the cell and converted into a concentrate that can then be processed in an autoclave or roaster to recover the gold. Bio-milling incorporates patented technology that involves inoculation of suitable crushed ore on a leach pad with naturally occurring bacteria strains, which oxidize the sulfides over a period of time. The ore is then processed through an oxide mill.

At Batu Hijau, ore containing copper and gold is crushed to a coarse size at the mine and then transported from the mine via conveyor to a concentrator, where it is finely ground and then treated by successive stages of flotation, resulting in a concentrate containing approximately 30% copper. The concentrate is dewatered and stored for loading onto ships for transport to smelters.

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