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1. Pretreatment of thiourea gold extraction materials
According to the experimental and industrial production practices of most researchers, thiourea is not sufficiently stable during the leaching operation, the consumption is too large, and the consumption of sulfuric acid is too much. It is uneconomical to leaching ore with a low gold content, so today's research is often used to treat concentrates with high gold content.
Although thiourea for complex processing difficulties refractory gold cyanide containing carbon, arsenic, antimony and muddy, silver ore, but some ore mining, mineral or due to the presence of certain substances interfere with the leaching process, so that The recovery rate of thiourea gold is not high. In order to improve the adaptability of thiourea to these ores and reduce the consumption of thiourea and sulfuric acid, many researchers have used oxidative roasting (or calcination) process to pre-treat the raw materials before thiourea leaching, and achieved satisfactory results. .
1) The adverse effects of carbon removal in the wet gold extraction process are well known. The most important thing is that it will adsorb the dissolved gold during the leaching process, and the gold-adsorbed carbon will be lost along with the leaching residue, thus reducing the recovery of gold.
For example, a gold concentrate of a mine contains 1.13% of carbon. During the leaching of thiourea, a layer of black matter is always floating on the surface of the slurry. The recovery rate of gold is only 72%-85%. After this, the concentrate is oxidized and calcined at 680-700 ° C for 20-25 min, and the carbon content is reduced to below 0.08%. Thereby eliminating the adverse effects of carbon and other substances, the recovery rate of gold is increased to 94%-96%.
2) changing the structure of the mineral phase and usually contains large amounts of gold concentrate pyrite, brass galena ore and the like, which are insoluble at acidic mineral Thiourea, addition of gold naturally associated with them or Coexist together. By calcination at a low temperature (600-700 ° C), most of the sulfur is oxidized to produce a loose porous structure of the calcine. Most of the oxidized sulfur generates SO 2 and partially reacts with copper, lead, iron and the like contained in the concentrate to form sulfate. If gold is selenium gold, hoof gold, and sulfide containing arsenic and antimony, an oxidation reaction will occur to dissociate the gold. Oxidized ore and semi-oxidized ore flotation concentrate, which contains a certain amount of malachite, azurite, leucite, siderite and limonite, etc., the presence of carbonate will not only increase the consumption of sulfuric acid, When the pulp is acid-adjusted to adjust the pH, a violent reaction will occur to generate a large amount of bubbles, and even the slurry overflows and affects the operation. Limonite (2Fe 2 O 3 ·3H 2 O) and goethite (Fe 2 O 3 ·H 2 O) are trihydrate and monohydrate hematite, containing 18.4% and 10.1% respectively. The presence of crystal water also hinders the dissolution of gold. By low-temperature oxidative calcination (satin burning), the carbonate is decomposed to form CO 2 to escape and the crystallization water is removed.
By oxidizing roasting, the phase and structure of the concentrate can be changed, and the natural gold is sufficiently exposed due to the loss of the carrier mineral, and is more easily leached. It not only accelerates the leaching speed of gold, increases the recovery rate of gold, but also reduces the consumption of thiourea.
3) Roasting operation conditions The calcination effect is affected by many factors, the most critical factors being the calcination temperature and time. If the temperature is too low or the time is too short, the oxidation degree of the raw material is not enough, the gold leaching recovery rate and the drug consumption can not be improved; on the contrary, if the temperature is too high or the time is too long, the generated oxides will combine with each other to form Cu, Pb, etc. The dense insoluble (or poorly soluble) oxides such as ferrite, silicate, magnetite, etc., which enclose natural gold, also reduce the leaching rate of gold. Therefore, for the raw materials of each mine, the best roasting operation conditions should be selected through experiments according to the equipment type and operation method. [next]
In addition, the roasting equipment and feeding method are also crucial. In China, the muffle furnace is mostly used for laboratory roasting. The single layer (or multi-layer) roaster is used for industrial production, and the indirect heating rotary kiln is used for the calcination of sulfate. Due to the high water content of the concentrate, it is often necessary to increase auxiliary operations such as drying to increase energy consumption and cost. Especially for muddy oxidized ore, the viscosity of the mineral material is large, the dehydration is difficult, and the water content of the filter cake is as high as 20% or more, which often causes the calcination to agglomerate and sandwich, which affects the leaching effect. In order to improve the roasting effect and improve the quality of the calcining, the Canadian Rhubarb Knife Gold Mine has successfully applied about 70% of the slurry containing solids to carry out slurry feed roking. Nowadays, this process has been widely used in many factories in Canada, the United States, Australia, Japan, Zimbabwe and other countries. The Central Plains smelter in China was officially put into operation in 1990.
4) Utilization of waste heat and flue gas The residual heat of oxidizing roasting is large, and rational use of it is an energy-saving measure. In modern times, heat pipe technology has been widely used, and heat pipe boilers can be built for heating and bathing. The calcined flue gas contains a high amount of SO 2 and can be used for pre-acidification of the pulp to save sulfuric acid.
2. Optimum acidity of thiourea extract
Thiourea has reducibility in acidic solution and is stable at pH 1-6. However, the stability of thiourea is different when different acids are added as pH adjusters. In view of the fact that thiourea is dissolved at low pH, the pH adjuster should generally be a strong acid capable of dissociating H + . Among the three strong acids, hydrochloric acid is highly corrosive, and the C1 2 /Cl - electric potential is 1.36V, and the oxidation ability is too strong. The potential of NO 3 - /NO for nitric acid is 0.96V, which is more than twice the potential of 0.42V for SCN 2 H 4 /(SCN 2 H 3 ) 2 , and the oxidation capacity is too strong. It is easy to make sulfur in solution. The urea is oxidized. Sulfuric acid SO 4 2- /SO 2 has a potential of 0.20V, which is much lower than the potential of 0.42V of thiourea to form dithiocarbamate. The oxidation capacity is weak, so sulfuric acid is the most ideal pH adjustment of thiourea solution. Agent. It can prevent the thiourea from being rapidly oxidized, and can dissociate H+ in a large amount to make the solution easy to reach the required pH, and the corrosion resistance of the device is also simpler. However, the addition of sulfuric acid to water is an exothermic reaction. Therefore, sulfuric acid should be added first when the slurry is prepared. After adjusting the pH, thiourea is added to avoid the oxidative loss of thiourea caused by the local temperature of the slurry being too high.
3. Slurry concentration, temperature and pressure
The operation of leaching gold and silver with an acid thiourea solution is usually carried out at room temperature and normal pressure. The test also proved that the initial dissolution rate of gold and silver increased with the increase of working temperature. However, the increase in temperature will accelerate the oxidation rate of thiourea in the solution, and the dissolution rate of gold and silver will decrease sharply with time. When the temperature rises to about 100 ° C, the thiourea will violently oxidize and fail. Therefore, the operating temperature of thiourea gold is mainly determined by the stability of thiourea, and the loss of thiourea during immersion in gold is minimized. So far, most researchers believe that it should be carried out at a temperature lower than or equal to 25 °C. However, it is also believed that this upper temperature limit is not necessarily optimal, and according to RG Schulzer's research, the German SKW method is to heat the slurry to 40 ° C to accelerate the oxidation of thiourea and introduce an appropriate amount of SO. 2 to maintain the dithiomethane state by controlling 50% of the total amount of thiourea in the slurry. It allows the precious metal to reach its maximum dissolution rate, and the consumption of thiourea can also be reduced to 0.57 kg/t (mine).
The concentration of the leached pulp is usually 1:2, but when the viscous oxidized pulp containing a large amount of slime is treated, the solid-liquid ratio can be appropriately increased.
According to the experimental and industrial production practices of most researchers, thiourea is not sufficiently stable during the leaching operation, the consumption is too large, and the consumption of sulfuric acid is too much. It is uneconomical to leaching ore with a low gold content, so today's research is often used to treat concentrates with high gold content.
Although thiourea for complex processing difficulties refractory gold cyanide containing carbon, arsenic, antimony and muddy, silver ore, but some ore mining, mineral or due to the presence of certain substances interfere with the leaching process, so that The recovery rate of thiourea gold is not high. In order to improve the adaptability of thiourea to these ores and reduce the consumption of thiourea and sulfuric acid, many researchers have used oxidative roasting (or calcination) process to pre-treat the raw materials before thiourea leaching, and achieved satisfactory results. .
1) The adverse effects of carbon removal in the wet gold extraction process are well known. The most important thing is that it will adsorb the dissolved gold during the leaching process, and the gold-adsorbed carbon will be lost along with the leaching residue, thus reducing the recovery of gold.
For example, a gold concentrate of a mine contains 1.13% of carbon. During the leaching of thiourea, a layer of black matter is always floating on the surface of the slurry. The recovery rate of gold is only 72%-85%. After this, the concentrate is oxidized and calcined at 680-700 ° C for 20-25 min, and the carbon content is reduced to below 0.08%. Thereby eliminating the adverse effects of carbon and other substances, the recovery rate of gold is increased to 94%-96%.
2) changing the structure of the mineral phase and usually contains large amounts of gold concentrate pyrite, brass galena ore and the like, which are insoluble at acidic mineral Thiourea, addition of gold naturally associated with them or Coexist together. By calcination at a low temperature (600-700 ° C), most of the sulfur is oxidized to produce a loose porous structure of the calcine. Most of the oxidized sulfur generates SO 2 and partially reacts with copper, lead, iron and the like contained in the concentrate to form sulfate. If gold is selenium gold, hoof gold, and sulfide containing arsenic and antimony, an oxidation reaction will occur to dissociate the gold. Oxidized ore and semi-oxidized ore flotation concentrate, which contains a certain amount of malachite, azurite, leucite, siderite and limonite, etc., the presence of carbonate will not only increase the consumption of sulfuric acid, When the pulp is acid-adjusted to adjust the pH, a violent reaction will occur to generate a large amount of bubbles, and even the slurry overflows and affects the operation. Limonite (2Fe 2 O 3 ·3H 2 O) and goethite (Fe 2 O 3 ·H 2 O) are trihydrate and monohydrate hematite, containing 18.4% and 10.1% respectively. The presence of crystal water also hinders the dissolution of gold. By low-temperature oxidative calcination (satin burning), the carbonate is decomposed to form CO 2 to escape and the crystallization water is removed.
By oxidizing roasting, the phase and structure of the concentrate can be changed, and the natural gold is sufficiently exposed due to the loss of the carrier mineral, and is more easily leached. It not only accelerates the leaching speed of gold, increases the recovery rate of gold, but also reduces the consumption of thiourea.
3) Roasting operation conditions The calcination effect is affected by many factors, the most critical factors being the calcination temperature and time. If the temperature is too low or the time is too short, the oxidation degree of the raw material is not enough, the gold leaching recovery rate and the drug consumption can not be improved; on the contrary, if the temperature is too high or the time is too long, the generated oxides will combine with each other to form Cu, Pb, etc. The dense insoluble (or poorly soluble) oxides such as ferrite, silicate, magnetite, etc., which enclose natural gold, also reduce the leaching rate of gold. Therefore, for the raw materials of each mine, the best roasting operation conditions should be selected through experiments according to the equipment type and operation method. [next]
In addition, the roasting equipment and feeding method are also crucial. In China, the muffle furnace is mostly used for laboratory roasting. The single layer (or multi-layer) roaster is used for industrial production, and the indirect heating rotary kiln is used for the calcination of sulfate. Due to the high water content of the concentrate, it is often necessary to increase auxiliary operations such as drying to increase energy consumption and cost. Especially for muddy oxidized ore, the viscosity of the mineral material is large, the dehydration is difficult, and the water content of the filter cake is as high as 20% or more, which often causes the calcination to agglomerate and sandwich, which affects the leaching effect. In order to improve the roasting effect and improve the quality of the calcining, the Canadian Rhubarb Knife Gold Mine has successfully applied about 70% of the slurry containing solids to carry out slurry feed roking. Nowadays, this process has been widely used in many factories in Canada, the United States, Australia, Japan, Zimbabwe and other countries. The Central Plains smelter in China was officially put into operation in 1990.
4) Utilization of waste heat and flue gas The residual heat of oxidizing roasting is large, and rational use of it is an energy-saving measure. In modern times, heat pipe technology has been widely used, and heat pipe boilers can be built for heating and bathing. The calcined flue gas contains a high amount of SO 2 and can be used for pre-acidification of the pulp to save sulfuric acid.
2. Optimum acidity of thiourea extract
Thiourea has reducibility in acidic solution and is stable at pH 1-6. However, the stability of thiourea is different when different acids are added as pH adjusters. In view of the fact that thiourea is dissolved at low pH, the pH adjuster should generally be a strong acid capable of dissociating H + . Among the three strong acids, hydrochloric acid is highly corrosive, and the C1 2 /Cl - electric potential is 1.36V, and the oxidation ability is too strong. The potential of NO 3 - /NO for nitric acid is 0.96V, which is more than twice the potential of 0.42V for SCN 2 H 4 /(SCN 2 H 3 ) 2 , and the oxidation capacity is too strong. It is easy to make sulfur in solution. The urea is oxidized. Sulfuric acid SO 4 2- /SO 2 has a potential of 0.20V, which is much lower than the potential of 0.42V of thiourea to form dithiocarbamate. The oxidation capacity is weak, so sulfuric acid is the most ideal pH adjustment of thiourea solution. Agent. It can prevent the thiourea from being rapidly oxidized, and can dissociate H+ in a large amount to make the solution easy to reach the required pH, and the corrosion resistance of the device is also simpler. However, the addition of sulfuric acid to water is an exothermic reaction. Therefore, sulfuric acid should be added first when the slurry is prepared. After adjusting the pH, thiourea is added to avoid the oxidative loss of thiourea caused by the local temperature of the slurry being too high.
3. Slurry concentration, temperature and pressure
The operation of leaching gold and silver with an acid thiourea solution is usually carried out at room temperature and normal pressure. The test also proved that the initial dissolution rate of gold and silver increased with the increase of working temperature. However, the increase in temperature will accelerate the oxidation rate of thiourea in the solution, and the dissolution rate of gold and silver will decrease sharply with time. When the temperature rises to about 100 ° C, the thiourea will violently oxidize and fail. Therefore, the operating temperature of thiourea gold is mainly determined by the stability of thiourea, and the loss of thiourea during immersion in gold is minimized. So far, most researchers believe that it should be carried out at a temperature lower than or equal to 25 °C. However, it is also believed that this upper temperature limit is not necessarily optimal, and according to RG Schulzer's research, the German SKW method is to heat the slurry to 40 ° C to accelerate the oxidation of thiourea and introduce an appropriate amount of SO. 2 to maintain the dithiomethane state by controlling 50% of the total amount of thiourea in the slurry. It allows the precious metal to reach its maximum dissolution rate, and the consumption of thiourea can also be reduced to 0.57 kg/t (mine).
The concentration of the leached pulp is usually 1:2, but when the viscous oxidized pulp containing a large amount of slime is treated, the solid-liquid ratio can be appropriately increased.
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