The calcination method is to decompose the gold- coated sulfide mineral into a porous oxide under the condition of high temperature aeration to expose the gold impregnated therein. The roasting method has been used as a pretreatment method for refractory gold ore for several decades. The method has wide adaptability to ore, simple operation and maintenance, and reliable technology. However, due to the conventional roasting treatment, toxic gases such as S02 and AS203 are released, and the environmental pollution is serious, so its application is limited. However, with the emergence of new roasting processes such as two-stage roasting, circulating boiling roasting, oxygen-enriched calcination, solidification roasting, flash calcination, microwave roasting, etc., the environmental pollution is reduced to some extent, the recovery rate of gold is increased, and the investment is increased. The production cost is correspondingly reduced, so that the roasting oxidation method becomes one of the priority schemes for the refractory gold ore pretreatment.
1 basic principle of roasting oxidation process
Under high temperature conditions, the following major chemical reactions will occur in refractory gold mines:
For pyrite:
3FeS2 + 8O2====Fe3304 + 6SO2 ↑ (5)
4FeS2 + 11O2====2Fe2O3+ 8SO2↑ (6)
For arsenic pyrite, when oxygen is insufficient and about 450 ° C:
3FeAsS==== FeAs2 + 2FeS + AsS ↑ (7)
12FeAsS + 29O2====4Fe3O4 + 6As2O3 ↑ + 12SO2 ↑ (8)
Above 600 ° C:
4FeAsS====4FeS + As4 ↑ (9)
As4 + 3O2 ==== 2As2O3 ↑ (10)
2 roasting oxidation process technology features
(1) The process has high processing speed and strong adaptability, especially for ores with organic carbon.
(2) By-products can be recycled and used to recover associated elements such as arsenic and sulfur.
(3) During the roasting process, it can cause "underburning" or "overburning" of the sulfide ore, which affects the leaching rate of gold.
(4) The roasting process produces a large amount of harmful gases such as dioxane sulfur and arsenic trioxide, and the dust collecting system is complicated.
(5) The process flow is long and complicated, the operation parameters are strict, and the production and debugging cycle is long.
(6) Influenced and restricted by the sulfuric acid market, fluctuations in acid prices directly affect the rationality of the process.
3 Development and application status of roasting oxidation technology at home and abroad
At present, the most common roasting oxidation process mainly involves two-stage boiling roasting of gold concentrate and solidified boiling roasting for ore.
For gold concentrates containing a considerable amount of arsenic, a two-stage roasting process is generally used, that is, a weak oxidizing roasting atmosphere or a neutral atmosphere is controlled at 400 to 450 Torr, and the arsenic-containing mineral is oxidized to form volatile arsenic trioxide, and the sulfur in the mineral is partially Oxidation; then oxidative calcination at elevated temperatures (above 500 ° C) to thoroughly desulfurize and carbon. The arsenic removal rate of the two-stage roasting is relatively high, and the residual rust of 0.2% ~ 0.5%.
In the mid-1950s, several gold mines used a two-stage roasting process to treat gold extraction from arsenic-bearing gold concentrates. The Swedish company Boliden has also developed its own unique technology. For example, the company's Helsingborg plant uses a two-stage roasting process for the treatment of arsenic-containing pyrite. One section is anoxic roasting, the air excess coefficient is 85% ~ 90%, and it is dilute phase roasting, that is, most of the calcining and flue gas enters the cyclone dust collector through the flue, and there is sublimated S2 & SO2 in the flue gas. As4, As4S6 and As2O3, in the cyclone dust collector, air is added to the air nozzle to continue the reaction, sulfur is converted to SO2, and arsenic is converted into As4O6. In fact, the cyclone dust collector can also be called the rear combustion chamber. A small amount of calcination in a section of furnace and a calcined sand from a cyclone collector enter the second stage furnace, and the second stage furnace is oxidized and roasted for further desulfurization, and the arsenic removal rate can reach 90% to 93%. China's Shandong Yantai Hengbang Smelting Co., Ltd. introduced the patented technology of two-stage roasting of arsenic-containing gold concentrate in Sweden in 2004. The Shaoguan smelting plant has also introduced this technology. In addition, the Central Plains Gold Smelter, Shandong Zhaoyuan University, Liaoning Xindu, Lingbao Gold Smelter, etc. are using the gold concentrate roasting process.
For the refractory gold ore roasting with poor floatability, sulfide minerals and gangue leans, the ore boiling roasting process is generally used, and the carbonate minerals contained in the ore are reacted with the sulfur and arsenic oxides generated during the roasting process. In the calcined materials, the sulfur and arsenic content in the flue gas is low, so the flue gas treatment is relatively easy.
The United States built the world's first solid arsenic-fixing sulfur ore roasting plant in the Cortez gold mine, which contains Au4.3g/t, As 0.12%, S 1.5%, Cl.0%. The process adopts a closed-circuit dry self-grinding system, which uses hot air to dry the ore powder and adopts a circulating boiling roaster. Since both grinding and roasting are in a closed loop state, the process conditions are easy to control, ensuring the leaching effect of gold, and the total recovery of gold is 80%. At present, there are more than ten raw ore roasting plants that have been put into operation abroad, and the ore properties and roasting processes are different. Ore grinding equipment basically uses dry grinding, some grinding systems with crushing + dry ball milling, such as Goldsrtrick gold mine; others using drying semi-autogenous grinding + dry ball milling grinding system, such as Minahasa Gold Mine. Some of the refueling of the roaster is made of coal , and some oils are used. In addition, gold concentrate is blended as a fuel.
China's ore boiling boiling roasting process has also achieved significant results. Based on the foreign boiling roasting and circulating boiling roaster, double-layer boiling roaster and other new process equipment, Changchun Gold Research Institute independently developed the “internal circulating boiling roaster†for the process mineralogy characteristics of difficult gold ore in China. "Innovatively adopts "under-oxidation high-temperature roasting technology", arsenic and sulfur "cure and self-cleaning" technology in roasting process, calcining "solid-gas exchange" waste heat utilization technology, and vertical roll grinding technology and equipment introduced into the cement industry for the first time. Thus, a new process for the extraction of gold from a raw ore-type dry grinding-boiling roasting-carbon slurry method with completely independent intellectual property rights is formed. Using this technology, the Zimuyu Gold Mine in Southwest Guizhou Province, which is fully representative and contains a large amount of refractory gold resources, was selected, and a roasting and gold-raising production plant with an annual processing capacity of 330,000 tons was built. After the raw ore of the Zimuyu gold mine is pretreated by boiling roasting, the gold leaching rate is increased from less than 10% of direct deuteration to over 82%. After the self-cleaning and solidifying effect in the roasting process, the solidification rate of arsenic in the ore is up to More than 98%, the curing rate of sulfur is over 90%.
The roasting method has the traditional advantage. With the advent of new devices such as the Lurgi cycle boiling furnace and the Poliden closed dust collection system, the two-stage roasting technology to process the gold concentrate will be developed in the future, and the technology of solid-arsenic-solid-sulfur roasting ore will have The great development, especially for the large-scale operation and development of difficult-to-select refractory gold mines, must adopt new roasting processes and devices to change the current situation of serious pollution caused by traditional roasting methods.
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