Thiourea, also known as sulfurized urea, white lustrous rhomboid crystal, tastes bitter, soluble in water, and aqueous solution is neutral. Thiourea can be used to immerse gold because gold can be dissolved in an acidic solution containing thiourea in the presence of an oxidizing agent: Au+2CS(NH 2 ) 2 ==== Au(SCN 2 H 4 ) 2+ +e    The use of cyanide in gold is not only harmful to the human body, but also pollutes the environment. Therefore, people are seeking non-toxic substitutes. The thiourea method is a immersion gold in this case. Process method. Due to the environmental pollution caused by cyanidation, a lot of research work has been done in the search for non-toxic and slightly toxic gold-immersed solvents for many years. Various non-cyanide methods have emerged. It is worth noting the thiourea method and the chlorination method. The most promising is the thiourea method. In the presence of an oxidizing agent, the method of directly dissolving gold as an acidic thiourea solution is referred to as thiourea method. Drill rig is an integrated system that drills wells, such as oil or water wells, or holes for piling and other construction purposes, into the earth's subsurface. The drill rig or drill machine we mean normally is the machine use to penetrate the surface of the earth's crust. For drilling, we supply small to medium drill rig, such as air track drill dth water drilling machine, anchor drilling machine, horizontal directional drilling machine, portable bore hole drilling machine, hydraulic drilling rig, underground water drilling rig, hydraulic geotechnical water well drilling rig etc. Drill Rig,Water Well Drill Rig,Hydraulic Portable Well Drill Rig,Diesel Engine Water Well Drill Rig Xi'an Heaven Abundant Mining Equipment CO.,LTD , https://www.tydrillingbits.com
The advantage is that the thiourea has low toxicity, the noble liquid is easy to handle, the thiourea can be regenerated and reused; the impurities in the gold ore are not easily dissolved; the leaching speed is fast. The disadvantage is that the price of thiourea is high, the consumption is large, and the cost is high; the consumption of sulfuric acid, and the corrosion of the equipment is severely leached in the acidic solution, and is not suitable for treating the alkaline ore. The operation is unstable, and the process of recovering gold from the thiourea solution still has technical problems to be solved.
The principle of gold dissolution is that in an acidic dilute thiourea solution containing high-valent iron ions, gold is oxidized and complexed with thiourea to form a cationic complex into the solution. Gold is oxidized and complexed and reacted as:
The leaching rate of thiourea dissolved in gold mainly depends on the pH value of the medium, the type and amount of oxidant, the amount of thiourea, the mineral composition and gold particle size, the leaching temperature, the leaching time and the immersion gold process.
Thiourea is unstable in alkaline liquid and easily decomposes into sulfide and cyanamide. However, thiourea is relatively stable in acidic media. Therefore, from the stability of thiourea, the thiourea dilute sulfuric acid solution is generally used as the leaching agent in the thiourea gold extraction, and it should be noted that the thiourea is added after the acid is added first, so as to prevent the thiourea from being hydrolyzed and failed due to the excessive local temperature of the slurry.
The acidity of the medium is related to the concentration of thiourea. The acidity decreases with the increase of thiourea concentration. The pH value of the medium is less than 1.5 under the condition of thiourea. However, the acidity should not be too large, otherwise the acid solubility of impurities will increase.
When thiourea dissolves gold, a certain amount of oxidant needs to be added. The preferred oxidants are manganese dicyanide , dithiocarbamidine, high-valent iron salt and dissolved oxygen. When the thiourea acidic solution is dissolved in gold, as long as the concentration of dissolved oxygen in the slurry is maintained, the high-priced iron salt can be regenerated.
Thiourea is an organic complex. It can form various cations with many metal cations in acidic solution. In addition to mercury , the stability of thiourea complexes of other metals is small, so thiourea acidic solution gold has high selectivity. . However, the copper and bismuth oxides in the raw material will be sour and complex with thiourea to reduce the thiourea leaching effect and increase the amount of thiourea. The raw material contains a large amount of acid solubles (such as ferrous iron, carbonic acid). Salts, non-ferrous metal oxides, etc.) and reducing components increase the consumption of oxidants and sulfuric acid and reduce the leaching rate of gold. Once copper, arsenic, antimony, lead and other sulfide minerals less harmful effects thiourea gold dissolution, thus an acidic thiourea solution gold dissolution can be extracted from a complex gold silver metal selectively refractory mineral raw materials.
Gold particle size is one of the factors affecting the gold leaching rate.
The sulphur urea dissolution rate increases with the leaching temperature, but the thiourea has low thermal stability. If the temperature is too high, it will be hydrolyzed and failed. The temperature of the slurry should not exceed 55 °C. Generally, the thiophene is extracted at room temperature.
The leaching rate of gold generally increases with the increase of the amount of thiourea. Since thiourea is mainly based on high-valent iron ions as oxidant, the high-valent iron ion concentration in the solution is much higher than the dissolved oxygen concentration and can be adjusted, so the thiourea dissolves gold. The concentration of thiourea is relatively high, and the amount of sulfur varies depending on the amount of gold contained in the raw material, and its unit consumption (kg/ton) is several kilograms to several tens of kilograms.
The leaching rate of gold generally increases as the leaching time increases.
The leaching rate of gold is related to the gold leaching process. The one-step method (such as carbon slurry method and carbon leaching method) can significantly shorten the gold leaching time. The thiourea method is a non-toxic gold extraction process, which has been adopted in China. This method is used to treat gold concentrates and flotation gold concentrates. However, this process still has a problem of high cost.
2Au+4CS(NH 2 ) 2 +Fe 2 (SO 4 ) 3 →{Au[CS(NH 2 ) 2 ] 2 } 2 SO 4 +2FeSO 4
At the same time, the thiourea will continue to be oxidized to form some other products, the first of which is methylated disulfide.
2CS(NH 2 ) 2 â†â†’NH 2 (NH)CSSC(NH)NH 2 +2H + +2e -
Metathyroid disulfide is a highly active oxidant which is believed to be necessary for the actual dissolution of gold. The methyl disulfide also forms thiourea and sulfinic acid compounds, which are finally decomposed into cyanamide and elemental sulfur. These reactions cause a loss of thiourea.