Gold and copper processing
Date: 2016-06-08Author: ZENITH
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.
For low-grade copper ore beneficiation need to go through to make the grade become enriched copper concentrate (issued by the Ministry of Metallurgical 1976 standard requires copper concentrate copper grade of 8 to 28%. In practice, the production of copper grade is generally 10 to 20%, the individual who had up to 30%), then concentrate to a smelting matte (copper sulfide and iron alloy, copper goods by flotation, and some with the use of magnetic separation, re-election or wet smelting.
For the correct selection of a variety of processing methods, to study the material composition and structural configuration of copper ore; identification of copper ore natural types and industry types; but also understand the refractory ore and mineral content of the general distribution and so on.
Natural copper ore containing different proportions of their general type copper oxide and copper sulfide, divided into sulfide ores (copper oxide containing less than 10%), mixed ores (copper oxide containing 10 to 30%) and oxidized ores (including oxide in more than 30% copper) three. Now commonly used in different types of copper ore beneficiation methods outlined below:
1. Single sulfide copper ore beneficiation. Commonly used flotation beneficiation.
2. polymetallic sulfide ore beneficiation. General characteristics of different processing techniques based on its main components formed were mixed flotation, flotation method, mixed priority flotation, flotation and beneficiation joint re-election law, flotation and magnetic separation beneficiation joint method, as well as joint flotation and hydrometallurgical processing.
3. Mix Ore. Usually flotation may be employed, it can be dealt with separately, or together with the sulfide ore processing; may also be combined with flotation and hydrometallurgical processing of copper concentrate which is to be elected, then after flotation flotation method tailings using hydrometallurgical processing.
4. oxide ore beneficiation. Usually flotation and hydrometallurgical joint process or segregation law and flotation processing; combination formula containing high copper oxide ore, usually with a hydrometallurgical process.
Second, copper ore copper ore beneficiation methods and quality requirements
Copper ore beneficiation major loss of activity and reduce the conversion rate. It is generally required content ARSENIC less than 0.3%.
Fluorine: hydrogen fluoride (HF) gas state into the furnace, sulfuric acid into the plant, production equipment corrosion damage. General requirements for copper concentrates in fluorine content of less than 0.1%.
Zinc: In a part of the smelting process of zinc oxide (ZnO) state into the slag, increase the viscosity of slag inclusions affect copper and copper melting; a part of the zinc sulfide (ZnS) state into the matte, matte was so viscous or foamy slag separation unfavorable. Further, when the temperature is lower than matte 1200 ℃, zinc sulfide (ZnS) is crystallized to form a copper furnace discharge port junction obstruction. It is generally required in copper concentrate zinc content of less than 6%; otherwise, the need for flotation.
Magnesium: magnesium oxide (MgO) state in the mineral magnesium, copper ore containing talc, serpentine, chlorite, magnesium and other high mineral olivine, easy mudding, flotation, the more surfaced together with copper minerals, sorting difficult, and easy to form the cake, so that the grinding process is not smooth. In addition, containing magnesium oxide (MgO) high after copper concentrate into the furnace slag to produce a viscous, higher melting point and cause quenching furnace. It is generally required in copper concentrate magnesium oxide (MgO) content of less than 5%.
2. The hydrometallurgical process is mainly applied to natural oxidized ores containing copper is not high or single ore. Because different leaching agent, but also point:
Sulfuric acid leaching - for processing high silica content of the acidic oxide ore;
Ammonia leaching - for processing large amounts of alkaline-containing minerals or natural copper oxide ore grade ore;
Bacterial leaching - for processing low-grade sulfide ore.
Third, the copper ore smelting of copper ores methods and quality requirements
Copper ore smelting methods are mainly pyrometallurgical, followed by hydrometallurgy. Select the smelting process mainly depends on the nature and physical components of the ore. It requires careful study of ore types, compositions of matter, the content of refractory mineral and harmful components zinc, arsenic, fluorine, magnesium and the like, mode of occurrence and distribution.
1. pyrometallurgical copper smelting is the most common method, it is divided into blast furnace, reverberatory furnace smelting, electric furnace smelting, flash smelting furnace, Noranda continuous smelting method. Low blast furnace efficiency, high power electric furnace smelting, reflection furnace smelting uses more, the latter two are relatively new smelting method.
Reverberatory furnace smelting copper concentrates mainly after flotation process, - as the requirements of copper concentrate grade of not less than 8%, preferably 15 to 20%.
Copper concentrates harmful impurities arsenic, fluorine, zinc, magnesium, etc., affect the smelting process and the pollution of the environment and health, when the ore into the furnace to be controlled, or be recovered in the smelting process.
Arsenic: oxidation states, is likely to be volatile in the smelting process, into the dust atmospheric pollution, harmful; after matte arsenic by converter blowing into the acid plant arsenic converter reconciling the catalyst gradually bit general 30 to 45%), after blowing matte become blister (copper grade of 97% to 99%), and then through the blister copper fire refining or electrolytic refining to obtain refined copper (copper grade of 99.9% or more). A small amount of rich copper ore (copper is generally greater than 5%) can without dressing, and mixed with copper concentrate directly into the furnace smelting.
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