Preparation method of a melamine-based low-toxic gold leaching agent

Abstract

The invention discloses a preparation method of a melamine-based low-toxic gold leaching agent, belonging to the field of hydrometallurgy. First, urea, sodium carbonate and ferrous chloride are mixed evenly and finely ground; then the finely ground material is placed in a high-temperature heating container, heated gradually and kept warm after the temperature is raised; then the reaction product is gradually cooled to room temperature along with the furnace; finally, the reaction product is broken and ground into powder to obtain the melamine-based low-toxic gold leaching agent. The synthetic raw materials of this gold leaching agent are simple and cheap and easy to obtain, the synthesis process is simple and easy to control, and the synthesis cost is low. The gold leaching agent obtained by the invention has low toxicity, fast gold leaching speed, high gold leaching rate, and the leaching tailings are general solid wastes and are easier to handle.

Description

Technical Field

[0001] The present invention relates to a preparation method of a low-toxic gold leaching agent, and particularly to a preparation method of a polymeric cyanamide-based low-toxic gold leaching agent. It belongs to the field of hydrometallurgy. Background Art

[0002] Due to advantages such as simple process, low production cost, and high gold leaching rate, the cyanidation method has always been the mainstream technology for gold extraction. However, cyanide is extremely toxic, and its use poses a huge environmental and safety risk. Therefore, the development of green and environmentally friendly non-toxic / low-toxic gold leaching agents is of great significance for the green and sustainable development of the gold industry. However, at present, non-toxic gold leaching agents such as thiosulfate, thiourea, thiocyanate, and glycine, which have been studied more at home and abroad, are rarely reported in industrial applications due to reasons such as low gold leaching rate, high reagent consumption, and difficult recovery of gold in the leaching solution.

[0003] In recent years, a series of new low-toxic gold leaching agent products have gradually emerged in the hydrometallurgy market in China, and some of these products have been relatively successfully applied industrially at home and abroad. According to literature reports, these new leaching agents are mainly obtained by high-temperature roasting of various chemical reagents, and their toxicity is lower than that of sodium cyanide, but their specific formulations and synthesis conditions have not been disclosed.

[0004] At the same time, several domestic invention patents have disclosed the synthesis and application of some new gold leaching agent products. For example, the invention patent application with the publication number CN111304456A discloses "an environmentally friendly gold extraction agent and its preparation method". This patent uses sodium carbonate, urea, sodium chloride, sodium sulfide, iodine, potassium ferricyanide, sodium thiocyanate, sodium bromide, and sodium thiosulfate as raw materials, and can obtain a low-toxic gold leaching agent by keeping warm at 700 - 800 °C for 1 - 5 h in a closed container. However, this patent has too many types of synthesis raw materials, resulting in a complex synthesis reaction process that is not easy to control, and a high synthesis temperature and long heat preservation time, resulting in too high synthesis costs.

[0005] For another example, the invention 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 mix urea and sodium carbonate and add them to a reactor. After heating to 120 °C, add activated carbon and iron catalyst. After reacting for 20 - 30 minutes, heat to 150 - 200 °C and continue to react for 20 - 30 minutes to obtain an intermediate product. Then, after maintaining the temperature of the intermediate product for 30 - 50 minutes, add sodium sulfate. After mixing evenly, heat to 300 - 350 °C and maintain the reaction for 0.5 - 1 hour to obtain a first-order reactant. After that, heat the first-order reactant to 450 - 500 °C and maintain the reaction for 1 - 1.5 hours to obtain a second-order reactant. Then, cool the second-order reactant to 200 °C and maintain the temperature for 20 - 30 minutes. Add sodium tripolyphosphate and sodium citrate, mix evenly, and then cool to room temperature to obtain a semi-finished product. Finally, crush the semi-finished product into powder, add sodium lignosulfonate, and mix evenly to obtain the gold leaching agent. Obviously, 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 invention 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 mix urea, sodium carbonate, ferrous salt, catalysts, and sodium cyanate and add them to a reaction vessel. After heating to the point where all the materials in the reaction vessel are melted, add sodium cyanate and maintain the temperature at 700 - 850 °C for 3 - 5 hours. Then, filter the impurities from the first-stage roasting product, introduce it into a receiving tray, cool it down, and add sodium bicarbonate, sodium citrate, thiourea, and sodium thiosulfate to obtain the gold leaching agent. Similarly, this method has complex types of synthetic raw materials, making it difficult to control the roasting process, and the heat preservation temperature is high and the time is long, so the synthesis cost is too high. In addition, the dosage of this gold leaching agent is relatively high when used for stirring leaching of gold concentrate.

[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 sodium ferrocyanide as raw materials, maintain the temperature 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 price of sodium ferrocyanide in the raw materials is expensive, and it will decompose to produce highly toxic sodium cyanide at the maintained temperature, resulting in a relatively high toxicity of the prepared gold leaching agent. In addition, the roasting temperature can reach up to 1000 °C, so the synthesis cost is relatively high.

[0008] In summary, the gold leaching agent synthesis methods reported in the prior art have technical problems such as a wide variety of raw materials, complex synthesis processes, high costs, high toxicity of the synthesized gold leaching agent, and large dosages. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a preparation method of a cyanamide-based low-toxic gold leaching agent, the prepared gold leaching agent has low toxicity, small dosage, good gold leaching effect, and the raw materials used in the preparation are simple in variety, cheap and easy to obtain, the synthesis process is simple, and the cost is low.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] A preparation method of a cyanamide-based low-toxic gold leaching agent is prepared according to the following steps:

[0012] (1) Mixing and fine grinding: Mix the raw materials urea, sodium carbonate and ferrous chloride evenly and finely grind them;

[0013] (2) Roasting: Place the finely ground material in a high-temperature heating container, gradually raise the temperature and then keep it warm;

[0014] (3) Cooling with the furnace: After the roasting is completed, gradually cool the reaction product with the furnace to room temperature;

[0015] (4) Crush and grind the reaction product into powder to obtain the cyanamide-based low-toxic gold leaching agent.

[0016] In step (1), the mass ratio of the urea, sodium carbonate and ferrous chloride is preferably 100:(33-135):(16-67). Further preferably 3:2:1.

[0017] In step (2), the roasting process conditions are preferably: the finely ground material is heated with the furnace, the heating rate is 5-20 °C / min, the holding temperature is 300-500 °C, the holding time is 5-30 min, and the roasting atmosphere is N2:O2 volume ratio (4-10):1.

[0018] The heating rate is further preferably 5-10 °C / min; the holding temperature is further preferably 400 °C, and the holding time is further preferably 10 min.

[0019] In step (3), the process conditions for cooling with the furnace are preferably: the cooling rate is 5-20 °C / min, and the cooling atmosphere is N2:O2 volume ratio 4:1-8:1.

[0020] The cooling atmosphere is further preferably N2:O2 volume ratio 4:1.

[0021] Preferably, the fine grinding particle size of the mixture in step (1) and the grinding particle size in step (4) are both 70-90% of -200 mesh.

[0022] The mechanism of the present invention is as follows:

[0023] A low-toxicity gold leaching agent of polycyanamide is prepared with urea, sodium carbonate and ferrous chloride as raw materials through a short process and at low cost. Among them, urea and sodium carbonate are reactants, and ferrous chloride is a catalyst. Under the catalytic action of ferrous chloride, urea and sodium carbonate first react at a relatively low temperature to form sodium cyanate. As the holding temperature increases, sodium cyanate undergoes a polymerization reaction under the catalytic action of ferrous chloride to form a polycyanamide gold leaching agent with a triazine structure. In this structure, the cyano group is fixed within a stable six-membered ring molecular skeleton and is difficult to dissociate into free cyanide ions, so its toxicity is low. The lone pair electrons of the active atom N in the cyano group on the skeleton can form a bond with gold ions, thus effectively leaching gold. During the roasting process, some divalent iron ions are oxidized to trivalent iron ions. During gold leaching, the low-concentration free cyanide ions dissociated from the polycyanamide gold leaching agent will coordinate with divalent and trivalent iron ions to form a stable and reversible redox couple Fe(CN)6 3- / Fe(CN)6 4- , which catalyzes the gold dissolution reaction, significantly shortens the leaching time, and improves the gold leaching rate.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The raw materials used in the present invention, namely urea, sodium carbonate and ferrous chloride, are all common agents on the market, with wide sources, non-toxic and low prices. Moreover, the low-toxicity gold leaching agent of polycyanamide can be synthesized only through a simple one-stage low-temperature roasting. The process is simple, the process is easy to control, and it is easy to promote and apply.

[0026] (2) The present invention uses ferrous chloride as a catalyst to catalyze the formation process of the intermediate product sodium cyanate and the final product low-toxicity gold leaching agent of polycyanamide, effectively reducing the reaction temperature and shortening the roasting time, thereby significantly reducing energy consumption and significantly reducing the synthesis cost. Moreover, by controlling the heating / cooling rate and roasting atmosphere, it is possible to avoid excessive changes in temperature and atmosphere causing the reaction to be too violent, resulting in product caking and decomposition and deterioration, and damaging the microstructure of the material, thereby effectively ensuring the product yield and performance.

[0027] (3) The low-toxicity gold leaching agent of polycyanamide obtained in the present invention has much lower toxicity than sodium cyanide. Its leaching tailings belong to general industrial solid waste, and the disposal cost will be greatly reduced. Moreover, during the leaching process, the catalytic effect of Fe(CN)6 3- / Fe(CN)6 4- on gold leaching is ingeniously utilized, so that the gold leaching rate is significantly increased. Under the condition of ensuring the gold leaching rate, the leaching time and the dosage of the agent are significantly reduced, and the gold leaching cost is reduced. Specific embodiments

[0028] The present invention will be further described below in conjunction with embodiments and experimental data.

[0029] The chemical composition (wt.%) of a certain gold-bearing oxidized ore is shown in Table 1 below. The following gold leaching experiments were all carried out using this gold ore for research.

[0030] Table 1 Chemical element analysis of gold-bearing oxidized ore / %

[0031]

[0032] Note: * The unit is g / t.

[0033] Example 1

[0034] Weigh urea, sodium carbonate and ferrous chloride according to Table 2, mix them evenly and grind them finely with a mortar to a ratio of 80% passing through -200 mesh. Place the finely ground material in a porcelain boat, then put it in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the temperature rises to 400 °C, keep it at this temperature for 10 min. The atmosphere during the heating and holding process is N2:O2 volume ratio of 4:1. After the reaction is completed, gradually cool the synthesized gold leaching agent to room temperature under the conditions of a cooling rate of 10 °C / min and an atmosphere of N2:O2 volume ratio of 4:1. Finally, take it out and crush and grind it finely to a ratio of 80% passing through -200 mesh. 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 12, leaching time 24 h.

[0035] The influence of the raw material ratio on the gold leaching effect of the synthesized low-toxic agent is shown in Table 2.

[0036] Table 2 Influence of raw material ratio on the gold leaching effect of the synthesized low-toxic agent

[0037]

[0038] As can be seen from Table 2, the raw material ratio has a great influence on the gold leaching rate. When the dosages of urea, sodium carbonate and ferrous chloride are 1 g, 2 g and 1 g respectively, the gold leaching rate is only 76.5%, and the free cyanide concentration in the leaching solution is also as low as 8.6 mg / L. With the increase of the urea dosage, the gold leaching rate gradually increases. After the urea dosage exceeds 3 g, the gold leaching rate begins to decline. When the urea dosage is certain, with the increase of the dosages of sodium carbonate and ferrous chloride, both the gold leaching rate and the free cyanide concentration show a law of first rising and then falling. The most suitable mass ratio of urea, sodium carbonate and ferrous chloride is 3:2:1. Under this condition, the gold leaching rate reaches 97.3%, and the free cyanide concentration in the leaching solution is 18.2 mg / L.

[0039] Example 2

[0040] Weigh urea, sodium carbonate, and ferrous chloride according to a mass ratio of 3:2:1, mix them evenly, and grind them finely in a mortar until the proportion of -200 mesh accounts for 80%. Place the finely ground material in a porcelain boat, then put it in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the furnace temperature rises to the temperature shown in Table 3, keep it at this temperature for 10 min. The atmosphere during the heating and holding process is N2:O2 with a volume ratio of 4:1. After the reaction is completed, gradually cool the synthesized gold leaching agent to room temperature under the conditions of a cooling rate of 10 °C / min and an atmosphere of N2:O2 with a volume ratio of 4:1. Finally, take it out and crush and grind it finely until the proportion of -200 mesh accounts for 80%. 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 12, and leaching time 24 h.

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

[0042] Table 3 Influence of the holding temperature on the gold leaching effect of the synthesized low-toxic agent

[0043]

[0044] As can be seen from Table 3, the holding temperature has a great influence on the gold leaching rate. When the holding temperature is 200 °C, the gold leaching rate is only 66.2%, and the free cyanide concentration in the leaching solution is only 5.3 mg / L. As the holding temperature increases, the gold leaching rate and the free cyanide concentration in the leaching solution increase rapidly. When the holding temperature is 400 °C, the gold leaching rate and the free cyanide concentration reach the maximum values of 97.3% and 18.2 mg / L respectively. When the holding temperature is further increased, the gold leaching rate and the free cyanide concentration gradually decrease.

[0045] Example 3

[0046] Weigh urea, sodium carbonate, and ferrous chloride according to a mass ratio of 3:2:1, mix them evenly, and grind them finely in a mortar until the proportion of -200 mesh accounts for 80%. Place the finely ground material in a porcelain boat, then put it in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the furnace temperature rises to 400 °C, keep it at this temperature for a certain period of time (as shown in Table 4). The atmosphere during the heating and holding process is N2:O2 with a volume ratio of 4:1. After the reaction is completed, gradually cool the synthesized gold leaching agent to room temperature under the conditions of a cooling rate of 10 °C / min and an atmosphere of N2:O2 with a volume ratio of 4:1. Finally, take it out and crush and grind it finely until the proportion of -200 mesh accounts for 80%. 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 12, and leaching time 24 h.

[0047] The influence of the holding time on the gold leaching effect of the synthesized low-toxic agent is shown in Table 4.

[0048] Table 4 Influence of heat preservation time on the gold leaching effect of the synthesized low-toxic agent

[0049]

[0050] As can be seen from Table 4, the heat preservation time has little influence on the gold leaching rate. When roasting for 5 min, the gold leaching rate reached 92.6%. As the heat preservation time increased to 10 min, the gold leaching rate increased to 97.3%. Therefore, the synthesis reaction proceeds very fast. Continuing to extend the heat preservation time, the gold leaching rate shows a downward trend.

[0051] Example 4

[0052] Weigh urea, sodium carbonate and ferrous chloride according to the mass ratio of 3:2:1, mix them evenly and grind them finely with a mortar until the proportion of -200 mesh accounts for 80%. Place the finely ground material in a porcelain boat, then put it in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the furnace temperature rises to 400 °C, keep it at this temperature for 10 min. The atmosphere during the heating and heat preservation processes is shown in Table 5. After the reaction is completed, gradually cool the synthesized gold leaching agent to room temperature at a cooling rate of 10 °C / min under the roasting atmosphere shown in Table 5. Finally, take it out and crush and grind it finely until the proportion of -200 mesh accounts for 80%. 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 12, leaching time 24 h.

[0053] The influence of roasting atmosphere on the gold leaching effect of the synthesized low-toxic agent is shown in Table 5.

[0054] Table 5 Influence of roasting atmosphere on the gold leaching effect of the synthesized low-toxic agent

[0055]

[0056] As can be seen from Table 5, the roasting atmosphere has a greater influence on the gold leaching rate. When the volume ratio of N2:O2 is 2:1, the gold leaching rate is only 42.5%. At this time, the free cyanide concentration in the leaching solution is also very low, only 2.1 mg / L. As the volume ratio of N2:O2 increases to 4:1, the gold leaching rate rapidly increases to 97.3%, and the free cyanide concentration in the leaching solution also increases to 18.2 mg / L. Further increasing the volume ratio of N2:O2, the increase in the gold leaching rate is not obvious.

[0057] Example 5

[0058] Weigh urea, sodium carbonate, and ferrous chloride according to a mass ratio of 3:2:1, mix them evenly, and grind them finely with a mortar until 80% of the particles pass through a 200-mesh sieve. Place the finely ground material in a porcelain boat, then put it in a muffle furnace and heat it up with the furnace. Adjust the heating rate (see Table 6). When the furnace temperature rises to 400 °C, hold it at this temperature for 10 min. The atmosphere during the heating and holding process is a volume ratio of N2:O2 of 4:1. After the reaction ends, gradually cool the synthesized gold leaching agent to room temperature under the conditions of a cooling rate of 10 °C / min and an atmosphere of a volume ratio of N2:O2 of 4:1. Finally, take it out and crush and grind it finely until 80% of the particles pass through a 200-mesh sieve. Use this synthesized gold leaching agent to leach the gold ore in Table 1. The leaching test conditions are: liquid-solid ratio of 2:1, dosage of low-toxic gold leaching agent of 0.05 wt.%, pH of 12, and leaching time of 24 h.

[0059] The influence of the heating rate on the gold leaching effect of the synthesized low-toxic agent is shown in Table 6.

[0060] Table 6 Influence of heating rate on the gold leaching effect of the synthesized low-toxic agent

[0061]

[0062] As can be seen from Table 6, when the heating rate is 5 °C / min, the gold leaching rate quickly reaches as high as 98.2%, and the free cyanide concentration in the leaching solution also reaches 20.1 mg / L. When the heating rate increases to 10 °C / min, the gold leaching rate slightly decreases to 97.3%, and the free cyanide concentration in the leaching solution is 18.2 mg / L. As the heating rate increases to 15 °C / min and 20 °C / min, the gold leaching rates decrease to 89.1% and 86.3% respectively, and the free cyanide concentration in the leaching solution also decreases rapidly. Therefore, too fast a heating rate is not conducive to the synthesis of the low-toxic agent.

[0063] Example 6

[0064] Weigh urea, sodium carbonate, and ferrous chloride according to a mass ratio of 3:2:1, mix them evenly, and grind them finely with a mortar until 80% of the particles pass through a 200-mesh sieve. Place the finely ground material in a porcelain boat, then put it in a muffle furnace and heat it up with the furnace at a heating rate of 10 °C / min. When the furnace temperature rises to 400 °C, hold it at this temperature for 10 min. The atmosphere during the heating and holding process is a volume ratio of N2:O2 of 4:1. After the reaction ends, cool the synthesized gold leaching agent to room temperature in two ways: natural cooling in the air and gradually cooling under controlled cooling rate conditions (see Table 6). Finally, take it out and crush and grind it finely until 80% of the particles pass through a 200-mesh sieve. Use this synthesized gold leaching agent to leach the gold ore in Table 1. The leaching test conditions are: liquid-solid ratio of 2:1, dosage of low-toxic gold leaching agent of 0.05 wt.%, pH of 12, and leaching time of 24 h.

[0065] The influence of the cooling method of the calcined product on the gold leaching effect of the synthesized low-toxicity reagent is shown in Table 7.

[0066] Table 7 Influence of the cooling method of the calcined product on the gold leaching effect of the synthesized low-toxicity reagent

[0067]

[0068] As can be seen from Table 7, the cooling method of the calcined product has a great influence on the gold leaching effect of the synthesized low-toxicity reagent. When the calcined product is directly taken out and naturally cooled in the air, the gold leaching rate of the low-toxicity reagent obtained is only 78.5%. However, when the furnace cooling method is adopted and the cooling rate is 5 °C / min, the gold leaching rate of the low-toxicity reagent obtained is as high as 98.2%. As the cooling rate gradually increases, the gold leaching rate decreases, but all exceed 90%. Therefore, adopting the furnace cooling method is beneficial to obtaining good gold leaching effect. This may be because the furnace cooling avoids the destruction of the microstructure of the product during rapid cooling, thus ensuring its yield and performance.

[0069] Example 7

[0070] Weigh urea, sodium carbonate and ferrous chloride according to the mass ratio of 3:2:1, mix them evenly and grind them finely with a mortar to a particle size where the proportion of -200 mesh is 80%. Place the finely ground material in a porcelain boat, then put it in a muffle furnace and heat it up with the furnace. The heating rate is 10 °C / min. When the furnace temperature rises to 400 °C, hold it at this temperature for 10 min. The atmosphere during the heating and holding process is N2:O2 with a volume ratio of 4:1. After the reaction is completed, gradually cool the synthesized gold leaching agent to room temperature under the conditions of a cooling rate of 10 °C / min and a calcination atmosphere of N2:O2 with a volume ratio of 4:1. Finally, take it out and crush and grind it finely to a particle size where the proportion of -200 mesh is 80%. Use this synthesized gold leaching agent and sodium cyanide to leach the gold ore in Table 1, and investigate the differences in its gold leaching rate and free cyanide concentration under different reagent dosages and leaching time conditions. The other leaching test conditions are: liquid-solid ratio 2:1, pH 12.

[0071] The gold leaching rate and free cyanide concentration under different dosages of low-toxicity gold leaching agents, sodium cyanide and leaching time conditions are shown in Table 8.

[0072] Table 8 Comparison of gold leaching effects between the synthesized low-toxicity reagent and sodium cyanide

[0073]

[0074] As can be seen from Table 8, 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 83.2%, 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 90.8%, while the gold leaching rate of sodium cyanide is only 85.6%, which is basically equivalent to the gold leaching rate of 86.5% of the low-toxic gold leaching agent at 12 h. Similarly, 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, faster leaching rate and higher gold leaching rate.

Claims

1. A method for preparing a polycyanamide low-toxic gold leaching agent, characterized in that Prepare according to the following steps: (1) Mixing and fine grinding: Mix the raw materials urea, sodium carbonate and ferrous chloride evenly and finely grind them; The mass ratio of the materials urea, sodium carbonate and ferrous chloride is 100: (33-135): (16-67); (2) Calcination: Place the fine abrasive in a high-temperature heating container, gradually increase the temperature, and then keep it warm; The roasting process conditions are as follows: the fine abrasive is heated with the furnace, the heating rate is 5-20 °C / min, the holding temperature is 300-500 °C, and the roasting atmosphere is N2:O2 volume ratio (4-10):1; (3) Furnace cooling: After the roasting is completed, the reaction product is gradually cooled to room temperature in the furnace; The process conditions for furnace cooling are as follows: cooling rate is 5-20 °C / min, cooling atmosphere is N2: O2 volume ratio 4:1-8:1; (4) The reaction product is crushed and ground into powder to obtain a polycyanamide low-toxic gold leaching agent.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of urea, sodium carbonate and ferrous chloride is 3:2:

1.

3. The preparation method according to claim 1, characterized in that In step (2), the insulation time is 5 to 30 min.

4. The preparation method according to claim 3, characterized in that: The heating rate is 5-10 ℃ / min; the holding temperature is 400 ℃ and the holding time is 10 min.

5. The preparation method according to claim 1, characterized in that: The cooling atmosphere was N2:O2 in a volume ratio of 4:

1.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The fine grinding particle size of the mixture in step (1) and the grinding particle size in step (4) are both -200 mesh, accounting for 70 to 90%.

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