Thiourea extraction gold and silver process (1)

When Jiabu La atmosphere of thiourea and a comparative test method was done, the two methods is treated with carbon-containing gold concentrate pyrite arsenic 500g, at 25 ℃, liquid to solid ratio of 2, using air as the oxidant (1L /min) and each of its optimal leaching parameters: thiourea method with 1000mL of TU solution containing 0.175moVL H ₂ SO ₄ , 0.197mL / L (15g / L); cyanide with 1000mL deionized water plus 4 g NaCN, and added Ca(OH) _{2 to} maintain pH = l0. Figure 1 shows that after 30 minutes of leaching by thiourea, the gold recovery rate is nearly 90%. At this time, the recovery rate of cyanidation gold is only 35%. To obtain 94% extraction rate, the cyanidation method takes 24 hours, while the thiourea only needs 1 hour. .

Glorywalde uses a sulfuric acid-thiourea solution for the leaching of gold from untreated or pickled ore. When the solution contains H ₂ SO _{4 at a} concentration of 1.0 mol/L, 1.2 mol/L sulfur. When urea and 0.1 mol/L of hydrogen peroxide, the gold dissolution rate is very fast, 98.5% of gold can be recovered in 1 h, and the consumption of thiourea is 1.4 kg/t ore.
Chen Dengwen leaches gold from refractory carbonaceous ore. After roasting and sulfuric acid pretreatment, the acid thiourea leaching gold recovery rate is 95%, thiourea and sulfuric acid consumption are 1.5-2 kg per ton of ore respectively. 70 kg.
Insitu Inc. conducted an in-situ leaching test in Victoria, Australia, in 1981. It has been reported that a mixture solution of thiourea, thiosulfate and ferricyanide was first used in a "push-pull" test to extract gold from a deep-covered alluvial deposit.
According to laboratory calculations, 1000kg dry material and 100kg wet material (35g gold), under the conditions of adding H ₂ SO ₄ 5kg, SO ₂ 0.5kg, H ₂ O ₂ (30%) 0.75kg, thiourea 1.05kg, The extraction rate of gold can reach 98% (80% in the leaching section and 10% in the thiourea washing section). After 3 stages of carbon adsorption, the recovery rate of gold is 97.86% (3 segments are 80%, 16.37% and 1.49 respectively). %), the total recovery of gold is above 95%.
In short, in recent years, foreign countries have shown great interest in extracting gold from thiourea, but they are more cautious. It is more generally believed that the thiourea method has the advantages of reducing environmental pollution, accelerating the rate of gold dissolution, reducing the interference degree of copper , zinc , arsenic and antimony , short process flow, low investment and simple operation, compared with the cyanidation method; Problems involving high economic efficiency, such as high equipment costs, have yet to be resolved. [next]
After a comprehensive analysis of a large number of theoretical and experimental research work, the Soviet scholar BB Rodriguez developed a principle process for the wet treatment of gold ore based on thiourea leaching. The process includes the following four main processes:
1 Agitated leaching of gold is carried out by using a regenerated, purified and sterilized acid thiourea solution.
2 The gold-containing leachate and the leach residue are separated by dense filtration.
3 Recover gold from the solution to obtain the corresponding product that meets the requirements of the refinery.
4 The recovered thiourea solution is further processed to regenerate the thiourea and remove impurities from the solution.
For recovering gold from solution, the following methods can be used: metal (zinc, lead , aluminum ) to replace the precipitate, alkali solution (NaOH, etc.) to destroy the complex, electrolytic deposition, adsorption on activated carbon and cation exchange resin.
The choice of recovery method depends primarily on the metal content of the solution. 1 For solutions with high gold and silver content and mass concentration greater than 500 mg/L, electrolysis should be used, which can regenerate thiourea at the same time; 2 pairs of gold mass concentration is less than 50mg/L, and silver mass concentration is 200-400. The mg/L solution has the most promising adsorption method, and the precious metal can be adsorbed on the activated carbon or on the cation exchange resin; 3 pairs of gold mass concentration is more than 50 mg/L, and silver mass concentration is more than 20 mg/L. The solution, when the adsorption method is not effective, that is, the degree of enrichment of the metal is low, the precipitation method can be replaced with a metal, and in this case, it is economically unsuitable to use the electrolysis method.
The thiourea gold extraction processes studied at present include: conventional thiourea leaching method, SKW method for introducing SO ₂ into leachate, iron slurry method with metal iron plate immersion, adsorption with activated carbon or cation exchange resin. A carbon slurry or a resin slurry method, and an electrowinning method in which a cathode and an anode plate are inserted into a leaching tank for electrolysis.
Most of the raw materials for gold extraction by thiourea are gold concentrates or calcined gold, and the operation technology is almost the same as that of cyanidation with compressed air. However, acid-resistant equipment is required. The method of recovering gold from the leached slurry mostly uses a ferrite method and a carbon slurry method.
Conventional thiourea diffusion method
This method is a conventional method for leaching gold and silver into a sulfuric acid (pH 1.5-2.5) sulfur vein slurry by blast stirring. The dissolved gold in the slurry is usually filtered and washed several times, and gold is recovered from the filtrate and the washing liquid by displacement, adsorption or electrolysis. It is similar to the CCD process of cyanidation. However, since the pulp is a strong acid sulfur vein medium, copper, lead, zinc, iron and other base metals will dissolve together with gold and silver to form sulfur vein ions, which not only makes the ion concentration in the pulp too high, but also consumes a large amount of sulfur veins. In particular, when used to treat sulfur concentrates, sulfur enters the solution to form sulfides such as H ₂ S, S, SO ₄ ^2- , HSO ₄ ^- and the like. Their mutual conversion allows the equilibrium concentration of H ₂ S (liquid) in the slurry to be about 0.1 mol, which causes a large amount of sulfide precipitates in the metal ions. In particular, gold and silver are vulcanized and precipitated in the slurry, or sulfur adheres to the surface of the ore to form a passivation, which will reduce the leaching rate of gold and silver, so that the end point of the sulfur vein leaching operation appears prematurely, and the leaching residue contains Gold is too high and causes losses. However, since the leaching rate of silver veins to silver is much higher than that of cyanidation, since 1982, the gold and silver mines in Colorado have used sulfur veins instead of cyanidation to leach silver from silver-containing tailings, which has achieved good results. . [next]
1) Leaching bare gold from stibnite concentrates The Hillgrove antimony deposit in New South Wales, Australia is an early-exploited deposit with an average width of 300-400 m. In 1969, the New East Australian Mining Company (NEAM) operated a small mine and plant.
The ore is a quartz vein type gold-bearing ore deposit. The main symbiotic minerals are pyrite, pyrrhotite, arsenopyrite, scheelite and chlorite. The ore contains Sb 4.5% and Au 9g/t. The produced ore is subjected to grinding, re-election and flotation, and the produced ore concentrate is sold to the smelting plant. The concentrate contains 30-40g/t of gold, and the smelter does not pay any compensation. In order to extract the gold, the factory has been tested by cyanidation, and the effect is not good. Later, when testing other solvents, it was found that thiourea can quickly leach the bare gold in the concentrate. In March 1982, a 1t/h small batch thiourea leaching workshop was established.
The workshop's treatment of antimony concentrates is only to recover the monomer dissociation gold, and does not seek higher gold recovery. Therefore, the higher thiourea and Fe ³⁺ concentration is used, and the immersion liquid and the concentrate are pre-mixed and pulped, so that the pure leaching time of each batch of concentrate can be shortened to within a minute. The gold in the leaching solution is adsorbed by activated carbon, and the gold-loaded charcoal containing 6-8 kg/t of gold is directly sold. After adsorbing gold, the thiourea solution is added with H ₂ O _{2 to} adjust the oxidation-reduction potential and then returned to the leaching process for recycling.
In the first few months of leaching with thiourea, there has been a loss of dissolved gold deposits, which was found to be caused by the adsorption of gold on the surface of chlorite minerals in the concentrate, so air addition is added during flotation. Agent 633 to inhibit chlorite and to add a small amount of diesel to the slurry prior to leaching. After these measures, the bare gold can be leached, the gold recovery rate in the concentrate is 50%-80%, and the thiourea consumption is usually below 2 kg/t.
The company also found that the arsenopyrite in the flotation tailings contained a large amount of gold, so it increased the arsate flotation circuit, and the produced arsenic concentrate contained As15%~20%, Sb 5%, Au 150-200g/t. The recovery rate of gold in tailings is 70%. To this end, a 600 t/d early tailings reprocessing plant was built in 1983 to recover 1-2.5 g of gold per ton of tailings.
2) Preparation of sterling silver from silver-containing raw materials In order to explore a new process for preparing pure silver from silver-containing raw materials, Zhang Jian et al. carried out thiourea leaching, complex crystallization and sintered crystals of silver-containing raw materials to prepare sterling silver. handicraft Research. As a result of the test, the recovery rate of silver is over 91%, and the purity of the product silver is 99.84%.
The raw material components used in the experiment were (%): Ag 0.91, AgCl 0.29, SiO ₂ 61.00, CaO 15.76, MgO 0.78, Fe ₂ O ₃ 1.81, Al ₂ O ₃ 1.75, K ₂ O ₃ 1.16, Na ₂ O 0.47, H ₂ O 3.30, volatiles 11.05, others 1.72.
In the small test, the raw material is ground to -2mm, 100g is placed in a 500mL beaker, 300mL of the distillate prepared by adding the second distilled water and the reagent pure agent to carry out the single factor experiment of each condition, and the comprehensive condition experiment is carried out according to the single factor experiment result. The optimum conditions are as follows: the concentration of SCN ₂ HQ is 0.52 mol/L, H ₂ SO ₄ is 1.18 mol/L, Fe ₂ (SO ₄ ) 3 is 0.004 mol/L, temperature is 60 ° C, stirring speed. 700r/min, leaching time 2.5h, filtered, washed, combined with washing solution and filtrate, and discarded. The silver leaching rate was 98.50%. [next]
Expand the experiment Under the above conditions, use tap water and industrial pure chemicals to expand the experiment by 10 times. As a result, the leaching rates of silver were 97.23% to 98.91%, respectively, and the results of the small test using the double distilled water and the reagent pure drug were reproduced.
The silver in the thiourea leaching solution is in the state of Ag(SCN ₂ H ₄ ) ₃ ⁺ complex ions. The single-factor experimental results of the crystallization of the complex showed that the temperature decreased from 15 ° C to 2 ° C, the crystallization rate increased from 70% to over 95%; the pH was between 0.5 and 3, the crystallization rate was above 80%, and the pH rose. The crystallization rate is only slightly increased. A black precipitate appeared when pH > 3.5. When the concentration of silver in the solution is 0.6~3.6g/L, the crystallization rate is slightly higher than 80%. As the concentration of silver increased, the crystallization rate decreased slightly, but there was no significant effect. On the basis of this, the selected crystallization conditions were a temperature of 2 ° C, a pH of 3, a mass concentration of silver in the stock solution of 0.78 g/L, and a crystallization ratio of silver of 93%. Among the three factors, the analysis of variance shows that the main factor affecting the crystallization rate is temperature.
The produced crystals were dried at about 100 ° C, and then heated to 1100 ° C to produce 99.84% of pure silver. If the crystals separated in the mother liquor are washed with low-temperature water to remove soluble impurities, the purity of the product can be improved. The mother liquor after crystallization is separated and can be returned for leaching of silver.
Although the experiment is a small exploratory test of 0.1-1.0kg scale, the production process is short, the process is simple, the equipment investment is small, the product purity is high, and it can be used to treat impure metallic silver, silver chloride, silver sulfide, silver ore, The angle silver mine and its mixed raw materials have industrial application prospects.
2.SKW method (also known as SO ₂ reduction method)
This method is a joint study of the German Southern German Cyanide Calcium Oxide Company (SKW), which introduces the reducing agent SO ₂ into the thiourea immersion gold system based on the conventional thiourea leaching method.
This method is based on the fact that the thiourea has poor stability and is easy to oxidize. In a solution containing a high Fe ³⁺ (mass concentration of 3-6 g/L), thiourea will fail due to the following reaction:

The above reaction was carried out in three steps. The first step is a reversible reaction. The thiourea can be oxidized to form dithiomethane, and the dithiocarbamate formed in the presence of a reducing agent can be reduced to thiourea. The second step is an irreversible reaction, in which dithiocarbamate is partially reduced to thiourea by disproportionation, and a sulfenide of unknown composition is partially formed. The third step is also an irreversible reaction, which is finally decomposed into cyanamide and elemental sulfur. The cyanamide can be further decomposed into urea. Due to this reaction, the amount of oxidative loss of thiourea in the immersion process is often many times higher than the pure consumption of the gold-soluble agent. And the elemental sulfur which is finally decomposed is sticky, and it covers the surface of all the solid materials to passivate them, so that the leaching rate of gold or the like is lowered. [next]
In order to overcome these difficulties, the irreversible decomposition of dithiocarbamate in the above reaction should be avoided, that is, the concentration of dithiocarbamate in the solution is prevented from being too high, or a reducing agent is added to reduce the dithiocarbamate to a thiourea through a reversible reaction. This idea is the basic guiding ideology of SKW law research.
Sulfur dioxide is a highly efficient reducing agent. Under the specific conditions of thiourea immersion gold, the researchers found that as long as dithiocarbamidine is present, it will not reduce other oxidants.
In the thiourea leaching test with 0.2-0.7mm silver particles, when the SO ₂ is not added, the surface of the silver particles is covered with a dark film, and the leaching rate of silver is about 25%, which is obviously the presence and initial concentration of Fe ³⁺ . Lower (0.5g/L). If excessive SO ₂ is supplied to the immersion liquid, the surface of the silver particles exhibits a bright metal state, and the dissolution rate of silver can reach 100%. When the amount of SO ₂ supplied is insufficient, the leaching rate of silver will decrease again.
When the same method is used to leaching gold particles, an unexpected phenomenon occurs, that is, when the amount of SO ₂ supplied is insufficient, the surface of the gold particles is bright, and the dissolution rate of gold is nearly 100%; and when excessive SO ₂ is supplied, The dissolution rate of gold decreases. However, this phenomenon can be explained by chemical kinetics.
It is proved by experiments that in the practical application of thiourea immersion gold, the temperature of the slurry is increased to 40 °C to accelerate the oxidation of thiourea to dithiocarbamate; and the SO ₂ is supplied to the slurry at an appropriate speed to reduce the excess in the slurry. Dithiocarbamidine. By controlling the supply rate of SO ₂ so that 50% of the total amount of thiourea in the slurry maintains the oxidation state of dithiomethyl hydrazine, high-speed leaching of gold and silver and reduction of thiourea consumption can be achieved. This measure is the key to the success of the SKW law.
Table 1 is a refractory oxidized ore containing Pb 50%, Zn 6.8%, Fe 26.5%, Ag 315 g/t, Au 10.6 g/t, respectively, using cyanidation method, conventional thiourea method and SKW method. Compare the results of the test. It can be seen from the table that the SKW method supplies 6.5 kg/t of SO ₂ into the thiourea leaching slurry. The leaching rate of gold and silver in 5.5 h is much higher than that of the cyanidation method and the conventional thiourea method, realizing gold, The high-speed leaching of silver reduces the consumption of thiourea to 0.57 kg/t. Since the sulphur urea consumption of the SKW method has dropped to such a low level and the leaching time is greatly shortened, it is not only economical for processing high-grade gold concentrate, but also for economical treatment of low-grade gold ore. of.

The gold and silver in the leachate can be adsorbed by activated carbon, strong acid cation exchange resin or thiol resin, and then desorbed with hot acid or thiourea solution. Since the amount of thiourea is so small, it is not necessary to consider recycling it.
The results of the SKW test show that:
1 increase the operating temperature to 40 ° C, can accelerate the oxidation of thiourea to dithiocarbamate;
â‘¡ feed rate control SO _2, SO ₂ by reduction of the reduction of excess formamidine disulfide thiourea, to 50% of the total pulp thiourea formamidine disulfide holding state, blunt prevented feedstock To obtain the highest gold and silver dissolution rate;
3 Supplying an appropriate amount of SO ₂ to reduce excess dithiocarbamate to thiourea, preventing irreversible chemical oxidative degradation loss in the concentration of dithiocarbamate in the slurry, to improve the regeneration and utilization of thiourea, and reduce the consumption of thiourea .
According to the results of the small test, RG Schulze uses the process test procedure of Figure 2. The test feed was 1.1 t (100 kg in water), the thiourea for leaching was from the recycle liquid, 1.05 kg of new thiourea was added to the thiourea wash section, and the oxidant used H ₂ O ₂ . The balance values ​​of the mass concentration of thiourea TU (g/L) and Au (mg/L) and the solution flow rate (L) during operation are also shown in the figure. The technical points and indicators of the operation are:

1 The raw material is 10% wet material, and the flotation concentrate of the sulfide ore or the oxidized ore which has been pre-acid washed removes more impurities and reduces the ore processing capacity;
_{2 The} total consumption of SO ₂ per ton of mine is 6.5kg. After leaching, the remaining SO _{2 is introduced} into the slurry to further reduce the dithiocarbamidine to thiourea and completely precipitate the sulfur formed by oxidation, providing stable performance for subsequent operations. Solution
3 The oxidant Fe ^{3+ for} leaching operation is obtained by acid dissolution of the raw material itself and oxidation of H ₂ O ₂ ;
4 After the thiourea is leached, the slurry is sent to the adsorption after one filtration. The Au and Ag contained in the filter cake were briefly washed with a hot (50 ° C) solution containing a thiourea concentration of 15 g/L, and then subjected to secondary filtration, and the filtrate was subjected to secondary adsorption and secondary washing. The filter residue was washed three times with the lean liquid, and the washing liquid was sent for three times. The final filter cake and waste liquid are neutralized with lime or alkaline stone and discharged into the tailings dam; [next]
5 The total amount of gold in the 1t dry material of the test feed was 35g, the recovery rate of gold in the leachate was 88%, the recovery rate of the two washes was 10%, and the recovery rate of the total leaching was 98%. In the final filter cake, the slag contained 0.7 g of gold, the liquid contained 0.05 g of gold, and the total loss gold was 0.705 g, and the loss rate was 2%. The loss in the slag is large. To increase the recovery rate, add water to the filtration equipment B and then wash the final filter cake once, and discharge it after the fourth adsorption (shown by the dotted line in the figure);
6 Recovery of Au and Ag in the noble liquid. If activated carbon is used for adsorption, the loading capacity is up to 100kg/t, which can be smelted or desorbed after satin burning. If ion exchange resin is used for adsorption, the loading capacity of the resin is smaller than that of charcoal. However, a small amount of concentrated thiourea solution can be used to desorb the rich gold liquid, and it can be sent to electrolysis or replaced. In this experiment, activated carbon adsorption was used. The adsorption recovery rate of gold was 80% for the first time, 16.37% for the second time, 1.49% for the third time, and the total adsorption recovery rate was 97.86%.
After the above-mentioned 1t scale process test, the industrial production process of the thiourea carbon slurry method given by RG Schulze is shown in Fig. 3. This process is very similar to the cyanide carbon slurry process. However, since the operation time of thiourea leaching gold is much shorter than that of the cyanidation method, the non-filtered carbon slurry method which adsorbs after leaching is used. Other conditions are similar to those described above for the process test procedure.

3. Iron slurry method ("dip-set" one-step method)
The iron slurry method is to insert a certain area (3m ² · m ³ · tank ^{-1 in the} test) into the slurry of the leaching tank when the thiourea is leached with gold, so that the ratio of dissolved gold, silver, copper, lead, etc. The iron metal ions are firmly deposited on the iron plate as micron-sized sulfides. Due to the faster deposition rate, it is generally necessary to scrape the gold mud once every 2 hours, and then insert it into the tank for further use.
This method is a non-filtration operation, equipment and operation are relatively simple, and the gold deposition recovery rate can be stabilized at 99% or above. It has been promoted and applied in some mines in China. [next]
The deposition of gold mud is still in the category of negative metal replacement. That is, H ₂ S in the slurry will adsorb on the surface of the iron plate and ionize H ⁺ with the dissolution of iron. Therefore, the ionization velocity of H ₂ S on the iron plate is much larger than the natural dissociation of H ₂ S in the slurry, thus making iron The concentration of S ₂ ^{- on the} surface of the plate is much higher than that inside the slurry. Therefore, the metal ions such as dissolved gold are vulcanized on the surface of the iron plate and the deposition rate is much higher than that inside the slurry. In a short time, the surface of the iron plate can be covered with a thick layer. The layer is sulfided. As long as the dissolution of iron does not passivate, the sulfide precipitation of metal ions such as gold, silver, copper, and lead can be performed normally quickly. Therefore, in the "golden mud" produced, the gold-containing grade is mainly determined by the amount of various metals in the raw material which are higher in potential than iron. Under normal circumstances, the gold content of gold produced is only 1%-5%. Moreover, the deposition of gold, silver and other sulfides on the iron surface is replaced by the dissolution of iron, so the iron plate used in the iron slurry method dissolves quickly (15 kg of ordinary steel plate per ton of concentrate or 5 kg of low carbon steel plate), sulfuric acid consumption. The amount is also very large, and it is necessary to frequently add acid to the slurry to keep the medium in a suitable acidic state.
1) Iron slurry process test In the early tests, the gold leaching index of thiourea leaching sulfur concentrate was much lower than the cyanidation method. Therefore, many researchers have believed that the thiourea method is only suitable for the treatment of components. Raw materials. Since the Changchun Gold Research Institute and the Beijing Nonferrous Metals Design and Research Institute have introduced the iron-immersed solid-phase iron (steel plate) into the thiourea leaching system, the leaching rate and recovery rate of gold have been greatly improved. Become a major measure of thiourea gold extraction. Under suitable conditions, it can obtain the same leaching index as the cyanidation process, and the leaching time is shorter than the cyanidation method.
In an acidic thiourea solution containing an oxidizing agent, not only gold or silver will dissolve, but also cerium metal oxides and sulfides such as copper, lead, and zinc will dissolve:
MeO+2H ⁺ →Me ²⁺ +H ₂ O
MeS+2H ⁺ →Me ²⁺ +H ₂ S
The H ₂ S formed by the dissolution of sulfides can also undergo a series of reactions under the action of the oxidant and the acid to form S, S ^2- , HSO ₄ ^- , SO ₄ ^2- and the like. They can also be converted to each other at different potentials and pH conditions. Under acidic conditions, H ₂ S can be regenerated by a reversible reaction to balance the sulfides in the solution. At this time, the equilibrium concentration of H ₂ S is about 0.1 mol/L, and these H ₂ S can react with dissolved Au ⁺ , Ag ⁺ , Cu ²⁺ , Pb ²⁺ , Zn ²⁺ etc. to form sulfide precipitates in solution. .
In this case, in the pre-gold leaching stage of the thiourea which does not reinforce the phase iron in the slurry, the amount of H ₂ S produced is small due to the small ion concentration in the slurry, and the amount of gold particles exposed on the surface of the concentrate is large and large. The concentration of thiourea is also large. Under the action of oxidant, the leaching rate of gold is faster and the dissolved gold content is increasing. However, as the leaching time prolongs, the concentration of metal ions in the pulp increases continuously, and the concentration of H ₂ S also increases, and the concentration of free thiourea decreases. An increase in the concentration of H ₂ S naturally dissociates more S ^2- and reacts with the dissolved gold (and other metal) ions to form a sulfide precipitate. As the precipitation of sulfides strengthens, the rate of increase of gold content in the leachate decreases, and gradually progresses to a balance between gold leaching and sulfide precipitation to reach the "end point". This end point is much earlier than the true leaching end point of gold in the raw material, so the gold leaching rate is only a little more than 90%, about 6% lower than the cyanidation method (see Figure 4). When solid phase iron is added to the slurry, the dissolved gold and other high-potential metal ions are rapidly recovered on the iron plate by reacting with S ^2- to form sulfide deposits. The leaching precipitation rate of gold in the figure increases linearly with the time of adding the iron plate. When iron is added at the same time as the leaching operation of the slurry, the recovery rate of gold leaching precipitation is basically the same as the cyanide leaching rate. For example, the leaching rate of the cyanide method is 96.10%, the leaching rate of the thiourea iron slurry is 96.06%, and the leaching rate of the gold hole bismuth sulphur gold concentrate by cyanidation is 89.63%. The leaching rate was 87.49%. The indicators of the two are quite close. Metal ions such as gold rapidly sulphide precipitation on the iron plate, which not only reduces the ion concentration in the slurry, but also prevents their concentration from being too high and causes the loss of gold in the slag, and is also released by the dissociation of metal ions in the complex cation. A large amount of thiourea is produced to increase the concentration of free thiourea in the slurry. [next]
Figure 5 is a comparison of the leaching rates of thiourea and cyanide at different leaching times. It can be seen from the figure that the thiourea method without iron added has a maximum leaching rate of about 52% after leaching for 16 h of gold due to the sulfide precipitation of gold, and the strengthening of the sulfide precipitation of gold slightly decreases with time. In the thiourea method of adding iron at the same time of leaching, the leaching rate of gold increases with time, and the final leaching rate is quite close to the cyanidation method. Table 2 is an example of the main components and leaching and recovery indexes of the sulphur urea iron leaching sulphur gold concentrate raw material.

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