| During the industrial production process and application of nitric acid,it will generate high concentrations of nitrogen oxides, and nitrogen oxides are harmful to environment which can not be discounted. Nitrogen oxide itself is a very strong oxidiative material. It has great potential to utilize this oxidant to reduce pollution by appropriate method.Cyanide tailings contain about 2.2g of gold per ton. Pretreatment of cyanide tailings is benefit to gold extraction. The cyanide tailings contain a large number of valuable metals.To effective utilization of resources, it's important to extract the valuable metals in cyanide residues by appropriate method.With access to a large number of literatures and previous works on this project, we have proposed to use PEG-300 to absorb NO2 in the presence of oxygen. The products PEG-NO2 are used to pretreat cyanide gold tailings, appropriate method was used to recover and reuse PEG. We have studied the mechanism of PEG absorption of NO2 by UV-visible spectroscopy and infrared spectroscopy. The results demonstrated that there are three stages in the process of adsorption of NO2:first, the free state NO2 was adsorbed on the PEG film surface; Then, NO2 passed through the film and formed nitrous acid ester with PEG; Finally, the structure gradually changed to a very stable structure, nitric acid ester.Experimental study showed that the adsorption efficiency was much higher when using the mixture of PEG-300 and water, only if a little PEG was present, compared with using water without PEGLiterature and experimental results both showed that NO2 was difficult to assimilate by water when the temperature was above 60℃. But adding a little PEG, even it is 60℃, it still have high adsorption efficiency to NO2.NO2 was absorbed by PEG, and formed PEG-NO2, which was stable and has a mild oxidation. In the pretreatment of gold cyanide residues using PEG-NO2 as oxidants, the effects of experimental parameters have discussed. Various operation parameters were investigated, such as stirring rate, reaction temperature, reaction time and oxidant dosage. The results showed that when the concentration of slurry was 100 g/L, stirring rate was 150 r/min, the reaction temperature was 70℃, reaction time was 1.5 h, and oxidant dosage was 110 mL, the cyanide leaching of iron tailings up to 92%. Through second electronic scanning and X-ray surface scanning, it is showed that after pretreatment the sulfur and iron content was greatly decreased, and the relevance of iron and sulfur was lower compared with cyanide tailings. It was indicated that the pyrite crystal structure was destroyed and oxidized.We request Zhongyuan Gold Smelter to do experiments of cyanide gold, under the condition of the liquid-solid ratio 5:1,pH=9-10, NaCN dosage:2.0-3.0 g/L, cyanide time for 24h,gold extraction rate increased from 66.44%to 99.25%, indicating that this technology can effectively improve the rate of cyanide gold extraction.The acid filtrate was collected, and we adjust its pH using ammonia with volume ratio 1/1 to remove metal ions in the form of hydroxide precipitation. The pH of acid filtrate was adjusted to 6.8, and stirring for 30 min under room temperature.After centrifugation, the supernatant which obtains the least amount of metal was vacuum distillation to recycle PEG. The experimental results showed that recovered PEG can also be used to adsorb of NO2 with high efficiency. We found that, in the same conditions, the absorption product can also be highly efficient oxidation of cyanide tailings.Finally, we design the program that uses product of PEG absorption NO2 to pretreatment gold cyanide tailings. The program of technical, environmental, economic feasibility analysis will help to broaden the ideas of comprehensive recovery of cyanide tailings. |
PDF Full Text Request