Preparation Method and Application of a Low-Toxicity and High-Efficiency Gold Leaching Agent

Abstract

The invention discloses a preparation method and application of a low-toxicity and high-efficiency gold leaching agent, belonging to the technical field of hydrometallurgy. Sodium cyanate and manganese dioxide are mixed evenly and then roasted, and then the roasted product is mixed with sodium citrate to obtain a polymeric cyanamide-based low-toxicity and high-efficiency gold leaching agent. The raw materials adopted by the invention are simple in variety, non-toxic, cheap in price, and the synthesis process is simple and easy to control. The prepared gold leaching agent has the advantages of low toxicity, good gold leaching effect, low dosage of the agent, etc., and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to a preparation method of a gold leaching agent, in particular to a preparation method of a low-toxic and high-efficiency gold leaching agent, and also relates to the application of the prepared gold leaching agent. It belongs to the technical field of hydrometallurgy. Background Art

[0002] Gold is a strategic metal with both commodity and currency attributes and plays an irreplaceable role in ensuring national economic security. Due to its advantages such as simple process, low production cost, and high gold leaching rate, the cyanidation method has long dominated the gold extraction industry. However, cyanide is a highly toxic substance and there are many restrictions in various links such as transportation, storage, and use. Therefore, it has become an urgent need in the gold industry to use non-toxic or low-toxic agents to replace sodium cyanide for gold extraction. There have been literature reports on the use of thiosulfate, thiourea, thiocyanate, etc. as non-toxic gold leaching agents. However, due to high gold extraction costs, complex gold recovery processes in leaching solutions, and difficulties in recycling gold extraction solutions, these non-toxic gold leaching agents have not been widely promoted and applied so far.

[0003] In recent years, some new gold leaching agent products have emerged in the Chinese market one after another. These new gold leaching agents are mainly obtained by high-temperature roasting of various chemical reagents, and their toxicity is lower than that of sodium cyanide. Some of them have been industrially applied at home and abroad, but the specific formulations and synthesis conditions are rarely disclosed.

[0004] In addition, several domestic invention patents have reported on the synthesis and application of some new gold leaching agent products. For example, the patent application with the publication number CN108441648A discloses "an environmentally friendly gold leaching agent and its preparation method", which uses 20 - 50% sodium carbonate, 10 - 50% urea, 1 - 10% sodium chloride, 1 - 5% sodium sulfide, 1 - 5% iodine, 1 - 5% potassium ferrocyanide, 1 - 5% sodium thiocyanate, 1 - 5% sodium bromide, and 1 - 5% sodium thiosulfate as raw materials, and is heated to 700 - 800 °C in a closed container and kept warm for 1 - 5 h to obtain the gold leaching agent. The main defects of this method are: the excessive variety of synthesis raw materials leads to a complex synthesis reaction process and is not easy to control, and the synthesis temperature is high and the heat preservation time is long, resulting in too high synthesis costs.

[0005] For another example, the patent application with the publication number CN116640922A discloses "an improved powdered gold leaching agent and its preparation method". Using urea, sodium carbonate, sodium sulfate, activated carbon, iron catalyst, sodium tripolyphosphate, sodium citrate, and sodium lignosulfonate as raw materials, first, urea and sodium carbonate are mixed and added to a reactor. After heating to 120 °C, activated carbon and iron catalyst are added. After reacting for 20 - 30 minutes, the temperature is raised to 150 - 200 °C, and the reaction continues for 20 - 30 minutes to obtain an intermediate product. Then, sodium sulfate is added to the intermediate product after maintaining the temperature for 30 - 50 minutes. After mixing evenly, the temperature is raised to 300 - 350 °C, and the reaction is maintained for 0.5 - 1 hour to obtain a first-order reactant. After that, the first-order reactant is heated to 450 - 500 °C, and the reaction is maintained for 1 - 1.5 hours to obtain a second-order reactant. Then, the second-order reactant is cooled to 200 °C and maintained for 20 - 30 minutes. After adding sodium tripolyphosphate and sodium citrate and mixing evenly, it is cooled to room temperature to obtain a semi-finished product. Finally, the semi-finished product is crushed into powder, and sodium lignosulfonate is added and mixed evenly to obtain the gold leaching agent. It can be seen that this method not only has too many types of synthetic raw materials, but also requires five-stage roasting, and the synthesis process is very complex, making it difficult to promote and apply.

[0006] For another example, the patent application with the publication number CN106399712A discloses "a low-toxic and environmentally friendly gold ore dressing agent and its preparation method". Using urea, sodium carbonate, ferrous salt, catalysts (activated carbon, nickel catalyst, iron catalyst), sodium cyanate, sodium bicarbonate, sodium citrate, thiourea, and sodium thiosulfate as raw materials, first, urea, sodium carbonate, ferrous salt, catalysts, and sodium cyanate are mixed and added to a reaction vessel. After heating until all the materials in the reaction vessel are melted, sodium cyanate is added again and maintained at 700 - 850 °C for 3 - 5 hours. Then, the impurities of the step roasting product are filtered off, and after being introduced into a receiving tray and cooled, sodium bicarbonate, sodium citrate, thiourea, and sodium thiosulfate are added to obtain the gold leaching agent. The types of synthetic raw materials in this method are complex, making it difficult to control the roasting process. Moreover, the holding temperature is high and the time is long, so the synthesis cost is too high. In addition, when this gold leaching agent is used for stirring leaching of gold concentrate, its dosage reaches 3 - 5 kg / t.

[0007] For another example, the patent application with the publication number CN102121067A discloses a "pollution-free ore dressing additive, its preparation method and application". Using sodium hydroxide, sodium carbonate, urea, and yellow prussiate of potash as raw materials, it is maintained at 600 - 1000 °C for 1 - 2 hours to obtain the gold leaching agent. The raw materials and synthesis process used in this method are relatively simple, but the yellow prussiate of potash in the raw materials is expensive and will decompose to produce highly toxic sodium cyanide at the holding temperature, resulting in a relatively high toxicity of the prepared gold leaching agent. In addition, the roasting temperature can reach up to 1000 °C at the highest, so the synthesis cost is relatively high. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a preparation method and application of a low-toxicity and high-efficiency gold leaching agent. The raw materials for preparing the gold leaching agent are non-toxic, simple in variety, simple in synthesis process, low in cost, and no toxic gas is generated during the production process, which is easy for industrial production; the synthesized gold leaching agent has low toxicity, and the original cyanidation gold leaching process does not need to be changed during the gold leaching process, and the dosage of the agent is small, the leaching speed is fast, and the gold leaching rate is high.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A preparation method of a low-toxicity and high-efficiency gold leaching agent is prepared according to the following steps:

[0011] (1) Raw material mixing: Mix sodium cyanate and manganese dioxide as raw materials evenly under sealed conditions;

[0012] (2) Roasting: Place the mixed material in a high-temperature heating container and carry out roasting under controlled atmosphere to obtain a roasted product;

[0013] (3) Preparation of gold leaching agent: Mix the roasted product with sodium citrate to obtain a low-toxicity and high-efficiency gold leaching agent.

[0014] Preferably, in step (1), the mass ratio of the raw materials sodium cyanate and manganese dioxide is 4:(0.5 - 1.5). The mass ratio of the raw materials sodium cyanate and manganese dioxide is further preferably 4:1.

[0015] Preferably, in step (2), the process conditions of the roasting are as follows: the mixed raw materials are heated with the furnace, the heating rate is 5 - 20 °C / min, the holding temperature is 450 - 550 °C, the roasting atmosphere is N2:O2 volume ratio of 4:1 - 8:1, and the holding time is more than 20 min. The heating rate is further preferably 10 °C / min; the holding temperature is further preferably 500 °C; the roasting atmosphere is N2:O2 volume ratio further preferably 6:1 - 8:1; the holding time is further preferably 20 - 60 min.

[0016] Preferably, in step (3), the mass ratio of the roasted product to sodium citrate is 100:(1 - 10). Further preferably 100:(3 - 10).

[0017] The low-toxicity and high-efficiency gold leaching agent prepared by the described preparation method is used for leaching gold in gold-containing raw materials including gold ore, anode slime and electronic waste.

[0018] The mechanism of the present invention:

[0019] Using sodium cyanate as the ligand source and manganese dioxide as the catalyst, at high temperature, both raw materials are in a molten state. Sodium cyanate undergoes a polymerization reaction, and manganese dioxide promotes the polymerization of sodium cyanate, ultimately generating a cyanuric acid-based gold leaching agent with a triazine structure. Since the cyano group is fixed within a stable six-membered ring molecular skeleton and is not easily dissociated into free cyanide ions, its toxicity is very low. The lone pair electrons of the active atom N in the cyano group on the skeleton can form a bond with gold ions, thereby achieving effective leaching of gold. Sodium citrate can react with harmful impurity metal ions such as Cu 2＋ 、Zn 2＋ 、Ca 2＋ 、Mg 2＋ in the leaching process to form chelates, dispersing gangue minerals, reducing their consumption of oxygen in the solution at the same time, increasing the content of "effective active oxygen" in the pulp, reducing the consumption of the gold leaching agent, and improving the gold leaching effect.

[0020] Advantages of the present invention:

[0021] Aiming at the problems of complex synthesis raw materials, high cost, difficult synthesis process control and easy generation of toxic gases for the existing synthesized low-toxic gold leaching agents, strong toxicity, large dosage and unsatisfactory leaching effect of the synthesized gold leaching agents, the inventors of this application have found through multiple experimental studies that a new type of cyanuric acid-based low-toxic gold leaching agent can be synthesized by only using two raw materials, sodium cyanate and manganese dioxide, through a one-stage low-temperature roasting. Then, by mixing with the additive citric acid, a new type of low-toxic gold leaching agent comparable to the gold leaching effect of sodium cyanide can be obtained. The present invention has the advantages of non-toxic and inexpensive synthesis raw materials, simple types, simple synthesis process, easy process control, no generation of harmful gases, low-toxic and environmental protection, fast leaching speed, high gold leaching rate, small dosage, etc., and has good potential to replace sodium cyanide for gold extraction. Specific embodiments

[0022] The present invention is further illustrated below with reference to examples and experimental data.

[0023] The chemical composition (wt.%) of a gold-bearing oxidized ore is shown in Table 1. The following gold leaching experiments were all carried out using this gold ore for research.

[0024] Table 1 Chemical element analysis of gold-bearing oxidized ore / %

[0025]

[0026] Note: * The unit is g / t.

[0027] Example 1

[0028] (1) Select sodium cyanate and manganese dioxide as raw materials, weigh a certain amount of sodium cyanate and manganese dioxide, and the raw material ratio is shown in Table 2. Put them in a sealed bag and shake well to ensure that the raw materials are fully mixed evenly.

[0029] (2) Transfer the mixed materials into a porcelain boat, and then place it in a muffle furnace to heat up with the furnace. The heating rate is 10 °C / min. When the temperature rises to 500 °C, keep it at this temperature for 30 min. The atmosphere during the heating and heat preservation process is N2:O2 with a volume ratio of 6:1.

[0030] (3) After the roasting is completed, place the product in the air and let it cool naturally to room temperature. After taking it out, mix it with sodium citrate at a mass ratio of 95:5 to obtain a low-toxic gold leaching agent.

[0031] (3) Use this synthesized gold leaching agent to leach the gold ore in Table 1. The leaching test conditions are: liquid-solid ratio 2:1, dosage of low-toxic gold leaching agent 0.05 wt.%, pH 11, and leaching time 24 h.

[0032] The influence of the raw material ratio on the gold leaching effect of the synthesized low-toxic agent is shown in Table 2.

[0033] Table 2 Influence of raw material ratio on the gold leaching effect of the synthesized low-toxic agent

[0034]

[0035] As can be seen from Table 2, the raw material ratio has a great influence on the gold leaching rate. When the mass ratio of sodium cyanate to manganese dioxide is 4:1, the gold leaching rate reaches the maximum value of 96.5%. Under this condition, the free cyanide concentration in the leaching solution is 32.3 mg / L.

[0036] Example 2

[0037] (1) Select sodium cyanate and manganese dioxide as raw materials. Weigh a certain amount of sodium cyanate and manganese dioxide according to a mass ratio of 4:1, and put them in a sealed bag and shake well to ensure that the raw materials are fully mixed evenly.

[0038] (2) Transfer the mixed materials into a porcelain boat, and then place it in a muffle furnace to heat up with the furnace. The heating rate is 10 °C / min. When the temperature rises to the set temperature in Table 3, keep it at this temperature for 30 min. The atmosphere during the heating and heat preservation process is N2:O2 with a volume ratio of 6:1.

[0039] (3) After the roasting is completed, place the product in the air and let it cool naturally to room temperature. After taking it out, mix it with sodium citrate at a mass ratio of 95:5 to obtain a low-toxic gold leaching agent.

[0040] (4) Use this synthesized gold leaching agent to leach the gold ore in Table 1. The leaching test conditions are: liquid-solid ratio 2:1, dosage of low-toxic gold leaching agent 0.05 wt.%, pH 11, and leaching time 24 h.

[0041] The influence of the heat preservation temperature on the gold leaching effect of the synthesized low-toxic agent is shown in Table 3.

[0042] Table 3 Influence of heat preservation temperature on gold leaching effect of synthesized low-toxicity reagent

[0043]

[0044] As can be seen from Table 3, the heat preservation temperature also has a great influence on the gold leaching rate. When the heat preservation temperature is 500 °C, the gold leaching rate reaches the maximum value of 96.5%. Under this condition, the free cyanide concentration in the leaching solution is 32.3 mg / L.

[0045] Example 3

[0046] (1) Select sodium cyanate and manganese dioxide as raw materials. Weigh a certain amount of sodium cyanate and manganese dioxide according to the mass ratio of 4:1, and put them in a sealed bag and shake well to ensure that the raw materials are fully and evenly mixed.

[0047] (2) Transfer the mixed materials to a porcelain boat, and then place it in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the temperature rises to 500 °C, adjust the heat preservation time at this temperature (see Table 4). The atmosphere during the heating and heat preservation process is N2:O2 volume ratio of 6:1.

[0048] (3) After the roasting is completed, place the product in the air and let it cool naturally to room temperature. After taking it out, mix it evenly with sodium citrate according to the mass ratio of 95:5 to obtain the low-toxicity gold leaching agent.

[0049] (4) Use the synthesized gold leaching agent to leach the gold ore in Table 1. The leaching test conditions are: liquid-solid ratio 2:1, dosage of low-toxicity gold leaching agent 0.05 wt.%, pH 11, and leaching time 24 h.

[0050] The influence of heat preservation time on the gold leaching effect of the synthesized low-toxicity reagent is shown in Table 4.

[0051] Table 4 Influence of heat preservation time on gold leaching effect of synthesized low-toxicity reagent

[0052]

[0053] As can be seen from Table 4, the influence of heat preservation time on the gold leaching rate is relatively small. When the heat preservation time is 30 min, the gold leaching rate reaches the maximum value of 96.5%. Therefore, the synthesis reaction rate is very fast. Under this condition, the free cyanide concentration in the leaching solution is 32.3 mg / L.

[0054] Example 4

[0055] (1) Select sodium cyanate and manganese dioxide as raw materials. Weigh a certain amount of sodium cyanate and manganese dioxide according to the mass ratio of 4:1, and put them in a sealed bag and shake well to ensure that the raw materials are fully and evenly mixed.

[0056] (2) Transfer the mixed materials into a porcelain boat, then adjust the roasting atmosphere as shown in Table 5, and then place the porcelain boat carrying the mixed materials in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the temperature rises to 500 °C, keep it at this temperature for 30 min.

[0057] (3) After roasting, place the product in the air and let it cool naturally to room temperature. After taking it out, mix it evenly with sodium citrate at a mass ratio of 95:5 to obtain a low-toxic gold leaching agent.

[0058] (4) Use the synthesized gold leaching agent to leach the gold ore in Table 1. The leaching test conditions are: liquid-solid ratio 2:1, dosage of low-toxic gold leaching agent 0.05 wt.%, pH 11, and leaching time 24 h.

[0059] The influence of the roasting atmosphere on the gold leaching effect of the synthesized low-toxic agent is shown in Table 5.

[0060] Table 5 Influence of roasting atmosphere on the gold leaching effect of the synthesized low-toxic agent

[0061]

[0062] As can be seen from Table 5, the roasting atmosphere has a great influence on the gold leaching rate. When the oxygen content is relatively high, both the gold leaching rate and the free cyanide concentration in the leaching solution are relatively low. When the volume ratio of N2:O2 is 6:1, the gold leaching rate reaches the maximum value of 96.5%, and the free cyanide concentration in the leaching solution under this condition is 32.3 mg / L.

[0063] Example 5

[0064] (1) Select sodium cyanate and manganese dioxide as raw materials. Weigh a certain amount of sodium cyanate and manganese dioxide according to a mass ratio of 4:1, and put them in a sealed bag and shake well to ensure that the raw materials are fully mixed evenly.

[0065] (2) Transfer the mixed materials into a porcelain boat, and then place it in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the temperature rises to 500 °C, keep it at this temperature for 30 min. The atmosphere during the heating and heat preservation process is a volume ratio of N2:O2 of 6:1.

[0066] (3) After roasting, place the product in the air and let it cool naturally to room temperature. After taking it out, mix it evenly with sodium citrate according to the mass ratio shown in Table 6 to obtain a low-toxic gold leaching agent.

[0067] (4) Use the synthesized gold leaching agent to leach the gold ore in Table 1. The leaching test conditions are: liquid-solid ratio 2:1, dosage of low-toxic gold leaching agent 0.05 wt.%, pH 11, and leaching time 24 h.

[0068] The influence of the addition amount of sodium citrate on the gold leaching effect of the synthesized low-toxic agent is shown in Table 6.

[0069] Table 6 Influence of Sodium Citrate Dosage on Gold Leaching Effect of Synthesized Low-Toxicity Agent

[0070]

[0071] As can be seen from Table 6, the sodium citrate dosage has a great influence on the gold leaching rate. When no sodium citrate is added, the gold leaching rate is 85.6%. With the increase of sodium citrate dosage, the gold leaching rate gradually increases. When the mass ratio of roasted product to sodium citrate is 95:5, the gold leaching rate reaches the maximum value of 96.5%. Continuing to increase the dosage of sodium citrate, the increase in gold leaching rate is not obvious.

[0072] Example 6

[0073] (1) Select sodium cyanate and manganese dioxide as raw materials. Weigh a certain amount of sodium cyanate and manganese dioxide according to the mass ratio of 4:1, and put them in a sealed bag and shake well to ensure that the raw materials are fully mixed and uniform.

[0074] (2) Transfer the mixed materials to a porcelain boat, and then place it in a muffle furnace to heat up with the furnace. The heating rate is 10 °C / min. When the temperature rises to 500 °C, keep it at this temperature for 30 min. The atmosphere during heating and insulation is N2:O2 volume ratio of 6:1.

[0075] (3) After the roasting is completed, place the product in the air and let it cool naturally to room temperature. After taking it out, mix it with sodium citrate according to the mass ratio of 95:5 to obtain the low-toxic gold leaching agent.

[0076] (4) Use this synthesized gold leaching agent and sodium cyanide to leach the gold ore in Table 1, and adjust the dosages of the synthesized gold leaching agent and sodium cyanide as shown in Table 7. The other leaching test conditions are: liquid-solid ratio 2:1, pH 11.

[0077] The gold leaching rates and free cyanide concentrations under different dosages and time conditions of the low-toxic gold leaching agent and sodium cyanide are shown in Table 7.

[0078] Table 7 Comparison of Gold Leaching Effects between Synthesized Low-Toxicity Agent and Sodium Cyanide

[0079]

[0080] As can be seen from Table 7, when the dosage of the gold leaching agent is 0.01%, after leaching for 6 h, the gold leaching rate of the low-toxic gold leaching agent reaches 86.5%, which is significantly higher than the gold leaching rate of sodium cyanide, 72.9%. With the increase of leaching time, the gold leaching rates of both gold leaching agents increase. When leaching for 24 h, the gold leaching rate of the low-toxic gold leaching agent reaches 92.2%, and the gold leaching rate of sodium cyanide reaches 87.6%, which is basically equivalent to the gold leaching rate of 88.3% of the low-toxic gold leaching agent at 12 h. In addition, under the conditions of the same dosage of the gold leaching agent and leaching time, the free cyanide concentration in the leaching solution of the low-toxic gold leaching agent is significantly lower. The gold leaching rates and free cyanide concentrations under other conditions of the dosage of the gold leaching agent and leaching time also basically follow the above rules. Therefore, compared with sodium cyanide, the low-toxic gold leaching agent synthesized in the present invention has lower toxicity and better leaching effect.

Claims

1. A method for preparing a low-toxic and high-efficiency gold leaching agent, characterized in that Prepare according to the following steps: (1) Raw material mixing: Mix the raw materials sodium cyanate and manganese dioxide evenly under sealed conditions; The mass ratio of the raw materials sodium cyanate and manganese dioxide is 4: (0.5-1.5); (2) Calcination: The mixed material is placed in a high-temperature heating container and calcined under a controlled atmosphere to obtain a calcined product; The calcination process conditions are as follows: the mixed raw materials are heated with the furnace, the heating rate is 5-20°C / min, the insulation temperature is 450-550°C, the calcination atmosphere is N2:O2 volume ratio is 4:1-8:1, and the insulation time is greater than 20 min; (3) Preparation of gold leaching agent: mixing the roasted product with sodium citrate to obtain a low-toxic and high-efficiency gold leaching agent; The mass ratio of the roasted product to sodium citrate is 100:(1-10).

2. The preparation method according to claim 1, characterized in that: The mass ratio of the raw materials sodium cyanate and manganese dioxide is 4:

1.

3. The preparation method according to claim 1, characterized in that: The heating rate is 10 °C / min; the holding temperature is 500 °C; the calcination atmosphere is N2:O2 volume ratio of 6:1 to 8:1; and the holding time is 20 to 60 min.

4. The preparation method according to claim 3, characterized in that: In step (3), the mass ratio of the calcined product to sodium citrate is 100:(3-10).

5. The low-toxic and high-efficiency gold leaching agent prepared by the preparation method according to any one of claims 1 to 4 is used to leach gold from gold-containing raw materials including gold ore, anode mud and electronic waste.

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