Our platinum group metal mineral resources are scarce, proven metal reserves just over 300 t. The associated platinum ore in Jinchuan copper- nickel ore mine in Gansu Province accounts for more than 60% of the total resources. The platinum-group metal mineral resources in Yunnan rank second in the country. Among them, the Jinbaoshan mine in Dali has proven platinum and palladium available for mining. The reserves are 45t, and the A+B+C+D reserves are 82t, accounting for 67% of the proven reserves in Yunnan Province. It is the first native platinum-palladium mine with industrial exploitation value discovered in China. The average grade of platinum and palladium in the Jinbaoshan Mine is 1. 4555 g·t - 1 , with a wide variety of minerals and very fine grain size. The average grades of copper and nickel are 0.14% and 0.22%, respectively, which are below the cut-off grade of industrial mining, while the MgO content affecting the melting temperature of fire is as high as 27%-29%. Ore phase analysis showed that the relative content of main minerals are: chalcopyrite 0.38%, 0.36% purple sulfur nickel ore, nickel 0.02% pyrite, pyrite 0.71%, 10.73% magnetite, ferrochrome Mines were 0.94%, while gangues such as olivine and serpentine were as high as 87.51%.
As platinum group metals are an important strategic resource urgently needed in China, relevant departments and metallurgical circles attach great importance to the research and development of Jinbaoshan platinum-palladium mine. In September 1997, the “Comprehensive Utilization of Low-grade Platinum and Palladium Resources in Jinbaoshan, Yunnan†project was approved to be included in the “Ninth Five-Year Plan†national key scientific and technological research project. At the end of 1998, the Guangzhou Nonferrous Metal Research Institute, which was responsible for the mineral processing research, first made breakthroughs. The successful flotation process allowed the recovery rates of platinum, palladium, copper and nickel to reach (%): 77.35, 76.93, 88.13 and 57.14. According to the process, a continuous expansion test was carried out with 25t of ore, and the produced flotation concentrate was provided by all relevant units in the research of the smelting process. The compositional analysis values ​​of the flotation concentrate mineral materials used by each unit are slightly different, and the chemical analysis results of the flotation concentrate components are listed in Table 1.
Table 1 Main components of gold ore obtained by continuous flotation in Jinbaoshan Mine
I. Several processes for handling Jinbaoshan flotation concentrate
(1) Wet extraction of platinum and palladium by microwave heating or sulfuric acid curing pretreatment
Ma Chong et al. briefly reported the results of wet extraction of metals from Jinbaoshan concentrate after microwave pretreatment for 10 min. The principle flow is shown in Figure 1.
Figure 1 Microwave pretreatment wet extraction process
The microwave frequency used for microwave pretreatment is 2450 MHz. The experiment was carried out in a microwave muffle furnace with a power of 1.5 kW. The study did not give the specific conditions of the two-stage leaching reaction and the components of the leachate. It is only indicated in general terms that the final leaching rates of Cu, Ni, Pt and Pd can reach (%): 98.89, 97.21, 87.95 and 95.43, respectively. According to the paper, microwave pretreatment can greatly reduce energy consumption compared with traditional roasting process, and the operation time is short, which can avoid harmful gas pollution. The process is simple and the construction scale can be large or small. Although microwave treatment has the characteristics of “rapid heating, uniform heating inside and outside and selective heating, thermal stress is generated between mineral grains, which leads to widening of intergranular cracks, thereby destroying the mineral crystal structure and changing the mineral phase and elemental valence state. , the purpose of opening the inclusions, but the results of microwave heating pretreatment of the concentrate showed that the effect is not good, so the microwave pretreatment in Figure 1 was changed to sulfuric acid pre-soak after sulfuric acid ripening. The optimum conditions for obtaining the pretreatment by orthogonal test are as follows: The amount of sulfuric acid after aging (mine:acid) is 1:0.5, the curing temperature is 150 °C, and the time is 10 h. The amount of pre-dip acid was 1:0.8, the liquid-solid ratio was 4:1, the temperature was normal temperature, and the time was 2.5 h. The prepreg can make the leaching rates of copper, nickel and cobalt reach 99.55 %, 98.74 % and 92.17%, respectively. The leaching rates of the second-order oxidizing acid leaching were 2.9 mol·L -1 , the oxidizing agent was 50%, the temperature was 95 ° C, and the time was 2.5 h. The leaching rates of platinum and palladium were reported to be 89.93 % and 89.26%, respectively. This article does not give the concentration of Fe, Mg in the acid leaching solution, the composition of the secondary oxidized acid leaching slag, and the content of other bismuth metals in the Pt and Pd leaching solution, so that it is difficult to understand the main component FeS of the concentrate sample. The direction of MgO.
(2) The process of smelting and collecting precious metals by fire method
At present, all well-known platinum group metal production plants at home and abroad use the fire method to smelt and collect precious metals into copper-nickel iron crucibles without exception. In this step, all silicate gangue and a large amount of iron sulfide, which account for about 70% of the concentrate, are discharged as slag. The copper-nickel iron crucible is oxidized and blown to obtain copper-nickel sorghum. The grade of platinum group metals in sorghum varies greatly depending on the flotation concentrate used by each manufacturer. The platinum group metal grade of copper-nickel sorghum in Jinchuan, China is only about 20 g·t -1 , while the sorghum produced by the Melunsky mine in South Africa can reach 3000 g·t -1 . For the treatment technology of sorghum, various domestic and foreign manufacturers have adopted different wet leaching processes, the purpose is to separate the copper-nickel bismuth metal, so that the platinum group metal grade in the leaching slag is further improved. For example, South Africa's Impala Company will use high-grade fine grinding and then use three-stage pressure leaching to obtain a precious metal concentrate with a platinum group metal plus gold grade > 45%. The company will separate the copper-nickel alloy from the sorghum by grinding 2 magnetic 2 floats, and then obtain the platinum group metal plus gold grade gold ore with about 60% of the precious metal concentrate by pressure acid leaching. Jinchuan's sorghum is too low in precious metal grade, and the copper-nickel alloy produced by the maglev is subjected to secondary vulcanization and secondary magnetic flotation separation. The obtained secondary copper-nickel alloy is leached and desulfurized by hydrochloric acid to obtain precious metal. Concentrate, and the precious metal grade only reached 13.87%. The Jinbaoshan research team basically inherited the technical route of traditional fire smelting, and the research proposed two process flows, as shown in Figures 2 and 3. For Flows A and B of Figures 2 and 3, the two processes from flotation concentrate to electric furnace smelting copper-nickel-iron are the same. The main difference is that Process B does not use oxygen to blow sorghum. In the process B, a section of the leachate cooled and crystallized product will contain 20% Ni, Co in the ferrous sulfate. If the ferrous sulfate is further processed, the process is more complicated, so the process A is preferred.
Figure 2 Flotation concentrate ore smelting process A
(III) New wet process for pressure cyanide after pressurized oxidizing acid leaching pretreatment
The problem of direct hydrometallurgy of flotation concentrates was discussed, and the possibility of direct extraction of platinum group metals by hydrometallurgy was negated. Although platinum group metals and cyanides can form stable cyanide anions, such as Pt (CN) 4 2 - , Pd (CN) 4 2 - ions, cyanide solution is difficult to etch metals under normal pressure at normal temperature. State of the platinum group metal. In the early 1990s, Bruckard et al. reported gold tailings after amalgamation with elevated temperature cyanidation. The gold mine is an oxidized ore containing high grade Au. Ore also contains Pd 0. 21 g · t Pt -1 and 0. 56 g · t -1 a. The results of the study showed that the leaching rate of Pt leaching was 75.4 %, Pd was 87.6 %, and the temperature was increased to 100 ° C, after immersing the amalgamated gold tailings with NaCN solution for 6 h under a nitrogen atmosphere of 80 ° C. The leaching rate can be increased to Pt 78.9 %, Pd 91.9 %.
Figure 3 Flotation concentrate ore smelting process B
In 2000, the authors studied the direct treatment of Jinbaoshan flotation concentrate by pressurized cyanidation. The constant total pressure was 2.0 MPa in air atmosphere, the reaction temperature was 160 °C, and the leaching rate of Pt was only 2718% after constant temperature stirring for 1 h. 63. 51%. Even if the flotation concentrate is pre-washed or wet-grinded, the cyanide leaching rate of Pt and Pd cannot be significantly improved. However, after in-depth study of the pretreatment method, it was found that if the refractory gold ore is treated, the flotation concentrate is fully oxidized and leached in an acidic medium, and then subjected to pressure cyanidation, and calculated according to cyanide residue. The leaching rate of Pt is > 95% and the leaching rate of Pd is >99%.
The new process flow of the pressurized cyanidation wet process proposed by us is shown in Figure 4.
According to the flow of Figure 4, a 50 kg volume autoclave was used to carry out an expansion test of 5 kg of batches. The results of three consecutive batches of pressurized oxidizing acid leaching are listed in Table 2; the corresponding Pt, Pd leaching rate is calculated according to cyanide slag. The results are shown in Table 3. The Pt and Pd recovery rates calculated from the Cu displacement slag solution and the Zn displacement slag solution are listed in Table 4.
Figure 4 Flotation concentrate concentrate wet processing new process
Table 2 Leaching effect of pressurized oxidized acid leaching metal
Table 3 Two-stage pressurized cyanide platinum and palladium leaching recovery effect (calculated according to the taste of cyanide slag)
Second, the discussion on several processes for processing Jinbaoshan flotation concentrate
(1) Wet process after microwave heating or sulfuric acid ripening
The effect of pretreatment of flotation concentrate by microwave irradiation for 10 min, the process of pre-soaking at room temperature after “cooking†for 10 h with sulfuric acid, this paper considers that the following main problems exist: (1) 18.32% Fe in flotation concentrate, 14.15 % S, 19.3 % MgO and about 5% CaO and Al 2 O 3 will react with sulfuric acid, and a large amount of harmful gases such as SO 2 and H 2 S will be generated at 150 °C, causing serious pollution; (2) Normal temperature preheating The concentration of Fe2 +, Mg2 + and Ca2 + in the immersion liquid has not been reported. Although the leaching rate of Cu, Ni and Co is still good, it is difficult to separate and extract. (3) The secondary oxidizing acid leaching requires leaching of Pt, Pd, which will consume a large amount of The oxidant increases the process cost; (4) The Pt and Pd leaching rate of the oxidized acid leaching is low. Due to the complex composition of the solution, the Pt and Pd concentrations are very low, and the precious metal enrichment is difficult to meet the refining requirements. In short, from the perspective of economic costs, environmental protection, operating conditions and technical indicators, there are a lot of problems in the above processes.
(2) Fire process smelting process
Although domestic and foreign platinum group metal manufacturers are using smelting and smelting to capture platinum group metals, the author believes that it is not a reasonable process for Jinbaoshan flotation concentrate mineral materials. The reasons are as follows: (1) Flotation concentrates with very fine particle size and high water content must be dried and sintered before being sent to the electric furnace, and the smelted low sorghum or sorghum must be crushed and ground before entering the wet process. Leaching treatment; (2) Since the MgO content in the concentrate is as high as 19%, the electric furnace in the process flow of Figures 2 and 3 must be added with Fe slag to prepare a suitable SiO 2 2MgO 2 CaO 2 FeO slag type, and the melting temperature is also high. 1350 ° C, and the low concentration of SO 2 flue gas produced by small-scale smelting is difficult to treat; (3) The effect of the process of Figure 2 is limited by oxygen blowing, and the residual Fe still needs P 2 O 4 extraction; By cooling crystallization to remove ferrous sulfate, the crystal will absorb 20% of Ni, Co, and the crystallization mother liquor still contains a considerable amount of Fe; (4) the precious metal enrichment obtained by the two processes, the platinum group metal Grade < 6 %, still can not meet the requirements of refining. From the overall perspective, the process of the two processes is very tedious, the cycle is too long, the recovery index of valuable metals is inevitably affected, and it is economically difficult to achieve efficiency.
(III) Advantages of pressure cyanide full wet process
It can be seen from Figure 4 that the all-wet process is a new process with few processes, short cycle, low energy consumption, low pollution and good operating environment. It has the following advantages: 1) The consumption of sulfuric acid by pressurized oxidizing acid leaching is only 10% of the concentrate. During the reaction, all sulfide minerals are converted into sulfates, and the leaching rates of Cu, Ni, and Co are all > 99%, and the sulfuric acid produced by the reaction is neutralized by alkaline gangue components such as MgO and CaO, so that the acidity of the leachate can be low. At pH = 2, a large amount of Fe3 + ions are hydrolyzed into the slag at high temperature, which is very advantageous for the separation of Cu, Ni, Co; 2) The slag rate of the pressurized oxidizing acid leaching is 50%, the particle size of the slag is fine, and the precious metal The coating of the ore particles is opened, which is beneficial to the subsequent leaching of the precious metals; 3) The two times of pressurization cyanidation process finally reduces the slag rate to 20%, and the precious metal ore particles which are covered by SiO 2 are also exposed, resulting in the leaching of Pt. The rate > 95%, the leaching rate of Pd is > 99%; 4) The precious metal is recovered from the pressurized oxidizing acid immersion liquid and the cyanide solution by a displacement method. The replacement slag is a noble metal enrichment with a high grade. The Pt,d grade in the Cu replacement slag is about 40%, and the impurities are mainly copper brought in by mechanical shedding. The Pt, Pd and other precious metals in the Zn replacement slag are 70% to 90%, which is very beneficial for the subsequent refinement of precious metals. From the data in Table 4, the average recovery of Pt obtained from the two slags is >94%, and the Pd recovery rate is ～99%. Such high expansion test technical indicators fully demonstrate the advanced nature of the new process.
Third, the conclusion
After briefly discussing several process flows for processing low-grade platinum ore flotation concentrates, compare the advantages and disadvantages of the three process options and their application prospects. Process scheme 1 has large consumption of chemical reagents, harmful gas pollutes the environment, Cu, Ni, Co is difficult to separate and Pt, Pd leaching rate is low, etc.; Process scheme 2 is cumbersome, high energy consumption, serious pollution, long cycle, precious metal The enriched items are low and economically difficult to be effective; Process Scheme 3 is more suitable for the treatment of platinum-palladium flotation concentrates with low grades in China, with high platinum-palladium recovery index, short process, low cost and no SO 2 pollution. . The whole wet process of pressurized cyanide after pressurized oxidizing acid leaching breaks through the traditional viewpoint of treating platinum-containing metal sulfide ore only by using fire smelting to effectively capture platinum group metals, and improving Jinbaoshan platinum ore resources. The comprehensive utilization level is of great significance. Therefore, based on the above discussion, it is considered that the most sustainable low-grade ore dressing enrichment and flotation concentrate smelting process is the third option, which is more realistic than the previous two programs.
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