Iodine gold extraction method and experimental study
I. Research status of foreign iodine gold extraction (I) Theoretical study Iodine is a highly oxidizing oxidant. With iodine and bromine as a leaching agent leaching agent for gold leaching process it should be the same, but few reports iodide leaching of gold, and no examples of industrial applications. However, according to the Russian Academy of Exploration noble metal complex anion [AX 2] (X is an anion) Stability comparison shows: CN -> I -> Br -> Cl -> NCS -> NCO -, gold iodide The strength of the complex is worse than that of the gold cyanide complex, but stronger than that of bromine, chlorine, thiocyanide or cyanate. And iodine is a non-toxic agent compared to cyanide. Therefore, it is suitable to study immersion of gold from ore with an iodine-iodide solution. Among the halogen elements, the AuI 2 - complex ion is most stable in an aqueous solution. Iodine can leach gold from ore at a lower concentration. Marun et al. used the thermodynamic data of Davis, Pourbaix and Latimer to map the Eh-pH relationship of the Au-I-H20 system, and proposed that two stable complexes were formed in the water stability limit: AuI 4 - and AuI 2 - . Among them, AuI 4 - is the most stable, and the two complexes are stable throughout the pH range, and the change of iodine concentration has little effect. When the iodine concentration is lowered and the pH is high, gold oxide species, gold and iodine are present. The network and area become smaller. At the same time, compared with the Eh-pH diagram of the Au-Cl-H20 system and the Au-Br-H20 system, it was found that both AuCl 4 - or AuBr 4 - were stable in a small region within the water stability limit. It can be said that AuI 4 - and AuI 2 - are the most suitable halides for the analysis of thermodynamic conditions. Marun et al. also calculated the equilibrium constants of the main reactions of the Au-I-I -- H20 system according to the study by Angelidis and Davis et al. Davis et al., through the interpretation of the equilibrium system, found that under different iodine and iodide concentrations The most stable species. At pH <8, I 2 and I - or a molar ratio of 0.35 to 0.1, most stable is I 3 -, AuI 2 and I -; at pH> 10, the most stable IO 3 -. If the molar ratio of I 2 to I - is 0.5, an insoluble gold iodide is formed at pH < 8, which inactivates the surface of gold and prevents the formation of AuI 2 - . Therefore, the actual work should be such that the molar ratio of I 2 to I - is less than 0.5. (II) Experimental study Marun et al. conducted two experiments on iodination immersion gold. Their sample samples were as follows: A sample containing Au was 8.29 g/t, Ag was 5.0 g/t, and Cu was 0.01%, the main association of gold minerals, alunite, hematite, gold, hematite, yellow copper ore - barite, gold - silicon, gold and enargite - Si - barite, when the 15nln the presence of free gold; sample B is a flotation concentrate containing Au was 57.69g / t, Ag was 39.49g / t, Cu 0.15%, mainly mineral pyrite, sphalerite, galena, and yellow Copper ore, gold is associated with quartz , and graphite is gangue. Both samples were ground to -0.074l and the masonry grade was 95%. Dip gold with iodine and potassium iodide reagent. The test conditions were determined as follows: the initial iodine, iodide molar ratio was less than 0.3, the pH was 3 to 5, and the standard reaction time was set to 4 h. The literature does not give gold leaching rate data, but the conclusion is that the gold leaching rate of cyanide leaching is high and the leaching time is long when compared with cyanide leaching. At the same time, the gold leaching test was carried out on the leaching rich liquid. The deposition rate of gold was over 90%, and the current efficiency was 0.12%-0.13%, which was basically independent of the initial concentration of iodine and iodide. Ce, Xenbnnxos FB et al. used iodine to conduct leaching studies on gold-bearing oxidized ore from a mine in Ural. Ore following chemical composition (%): 50.4 SiO 2, 15.8 Al 2 O 3, 16.4 Fe 2 O 3, 0.75 MnO, 2.46 MgO, 1.5 CaO, 0.63 Na 2 0,2.73 K 2 0,0.21 C, 0.03 S, 0.08 As, 3.5g/t Au, 9.0 other, gold is basically in a natural state but fine in particle size (0.01~0.03mill); gold is dissolved in iodine solution with a molar ratio of I 2 to I - 0.1, pH is 5.5-7.5 The ratio of solid to liquid is 1:5. When the reaction equilibrium is balanced, the recovery rate of gold is 95%, and the equilibrium speed is slower than that of bromine solution. When electroplating, the higher the concentration of gold, the faster the electrolysis speed, and the maximum deposition rate of gold can reach 95% (the concentration of gold in the electrolyzer is greater than 40mg/L). Second, the author's research on iodine gold extraction The research on iodinated gold leaching started late. Whether it is theoretical research or gold immersion process research, it is very imperfect and not systematic. In response to the existing problems, the author conducted a systematic study on the theory and process of iodized immersion gold. (1) Theoretical study The authors have drawn the Eh-pH diagram of Au-I-H2O by the actual immersion gold system (with the help of oxidant hydrogen peroxide), which is higher than the Eh-pH diagram of the Au-I-H2O system reported in foreign literature. More perfect and more practical. At the same time, the Eh-pH diagram of the Au-I-H2O system aimed at the determination of AuI precipitation was drawn. The study showed that AuI precipitation occurred in the solution when the concentration of iodine and iodide ions was high, but in the normal gold leaching process. In the middle, due to the low content of gold, the concentration of iodide ions and iodine is low, AuI precipitation does not occur in the solution. When the kinetics of leaching gold iodide, kinetic equation derived during gold leaching gold iodide dissolved reflected formula dissolution rate of gold and I -, I 3 - between, oxidant concentration and mixing intensity The relationship has theoretical guiding significance for the practice of iodized gold immersion. By thermodynamic calculation mechanism of leaching gold iodide analyzed, during the immersion gold iodide, I - and I 3 - views must simultaneously acting with gold, and gold iodide complex ions of the type generated for AuI, unified Iodide immersion gold chemical reaction formula and reaction product. The reaction behavior of impurities in the iridized gold leaching system was analyzed. It was pointed out that the sulfides, copper minerals, antimony minerals and carbonaceous minerals which are harmful to the cyanidation process are less harmful in the process of iodination. Much, the iodization method is highly adaptable to mineral types. In the process of iodination, as long as the oxidation potential of the oxidant is greater than 0.58V, the leaching rate and leaching rate can be increased during the iodination of gold; the equilibrium constant criterion and the reaction free energy criterion for the smooth progress of the reaction are derived. Formula, and based on this, it is judged that hydrogen peroxide can be used as the oxidant of the iodination leaching process, which can make the reaction proceed smoothly. The reason why the hydrogen peroxide promotes the gold dissolution reaction is that the dispersion is uniform, the diffusion is fast, and other minerals can be oxidized to inhibit the consumption of reagents. Going on. (Ii) Experimental Study of Guizhou Getang carbonaceous gold ore and carbonaceous oxidation original ore samples were sorted and iodide leaching test conditions. The gold-bearing minerals in the ore sample are dispersed, including sulfides, oxides, organic materials, gold, and gangue minerals. The gold is very finely embedded. It has been proved by flotation test that the gold grade of flotation concentrate cannot be effectively enriched, and the grade of tailings is not significantly reduced. Only the original ore should be leached or roasted. The leaching rate of cyanide direct leaching gold is less than 80%. It is leached with iodine and iodide (potassium iodide, sodium iodide and ammonium iodide) solution. The direct leaching rate of oxidized ore gold is up to 95%, with an average of 91%. Left and right, above 75.70% when cyanide leaching. The leaching time is 4 h, the liquid-solid ratio is 3:1 to 5:1, and it is leached in the neutral and acidic pulp under normal temperature conditions.
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