Typical Heavy Metal Pollution Identification, Prevention And Control Countermeasures In Nickel And Cobalt Smelting

Nickel and cobalt went by the name of the industrial MSG or industrial teeth,which were one of the important strategic resources and widely used in industry. It was not only had characteristics such as complex process and many pollutant discharge nodes, but also it was extremely difficult to control the pollution in nickel and cobalt smelting process. Especially the situation of the heavy metal pollution generated during smelting becomes more and more severe. Therefore, accelerating the research on prevention and control technology, identifying typical heavy metal pollution and reducing environmental pollution would be play a positive role for securing the interests of people on the environment, ensuring environmental security and promoting social harmony and stability.Our country had strengthened the research and management on heavy metal pollution of nickel and cobalt smelting industry with these problems had been paid more and more attention. Ministry of Environmental Protection had released standards of pollution prevention and control and technology policies for nickel and cobalt smelting industry. However, it has not yet formed a targeted and systematic system for it;existing regulations could not meet its requirements, which made its work difficult to carry out effectively. In view of this, typical nickel and cobalt smelting enterprises were taken as the research object this article, aimed at performing the investigation and monitoring of pollutant discharge nodes of nickel and cobalt smelting enterprises,analysed major characteristics of heavy metal pollutants discharge, defined the pollution sources on this basis. An inorganization discharge model of smoke & dust containing heavy metals in nickel pyrometallurgical process was studied. Finally, drew up the supervise schemes and suggestions of main heavy metal pollution sources for providing technical support to prevent and control of heavy metal pollution in nickel and cobalt smelting, which would be play a key role in the process of sustainable development of nickel and cobalt smelting enterprises.The production capacity of those enterprises had surveyed and measured accounted for more than 85% of entire nickel production enterprises, which played an important role and were typical representative of production processes and the pollutant generation and discharge in China's nickel and cobalt smelting industry. The paper had surveyed and measured five major nickel smelting enterprises including Jinchuan Group co., Ltd, Kalatongke Copper-nickel Mine, Xinjiang Xinxin Mining Industry Co., Ltd,Jilin Jien Nickel Industry Co., Ltd, and Jiangxi Jiangli Sci-Tech Co., Ltd. Combination production processes included that ? blastfurnace smelting + converter blowing produced high nickel matte, ?oxygen-rich top-blowing + settling electric furnace +converter blowing produced high nickel matte, ?electric furnace smelting + converterblowing produced high nickel matte, ?flash smelting + converter blowing produced high nickel matte, ?the first high grade nickel matte separating + nickel melt casting +nickel electrolysis produced electroreflned nickel, ?pressure-leaching produced nickel electrowinning, and ?the production process of leaching with sulfuric acid at normal pressure + nickel hydroxide + extraction electrowinning. Major cobalt hydrometallurgical enterprises had surveyed and measured in this paper included that Jinchuan Group co., Ltd, Zhejiang Galico Cobalt & Nickel Material Co., Ltd, and Jiangxi Jiangli Sci-Tech Co., Ltd. Combination production processes included that cobalt chloride, cobalt electrodeposition, cobalt hydroxide, and cobalt oxalate.The article focused the investigating and researching on 11 production lines of 7typical enterprises, which included all typical production processes of cobalt salt and electrical cobalt, high nickel matte and electroreflned nickel produced by nickel sulphide ore were also included. After that heavy metal pollution of discharge nodes had identified, there were mainly covered eight kinds of typical heavy metal in pollutant discharge nodes of all processes such as Cu, Pb, As, Cr, Cd, Co, Hg, Ni. The main heavy metal pollutant sources were analysed, so we got heavy metal pollutants nodes and its detailed list need to focus on: ?the prevention and control nodes of wastewater containing heavy metal included that impurity extraction with P204, copper deposition,nickel deposition, separating nickel and cobalt, impurity with P507, dechlorination, CN filters, ion recovery, alkaline washing, filtration washing; ?the prevention and control nodes of exhaust gas containing heavy metal included that blastfurnace, oxygen-rich top-blown smelting furnace, electric furnace, flash smelting furnace, reverberatory furnace, dilution furnace, settling electric furnace, converter, rotary kiln, sulfuric acid making process; ?the prevention and control nodes of waste residue containing heavy metal included that blastfurnace, flash smelting furnace, settling electric furnace.During the roasting and smelting process of copper-nickel sulfide ore, some of the heavy metals such as Pb, Cd, As, Hg, Cr, Zn, Cu, and Ni entered the dust after oxidation or sublimation, and other into the smoke, resulting environmental pollution in those processes. By collecting the recovery dust in exhaust gas from preparation section,smelting furnace and Converting furnace in 4 nickel smelting enterprises, component analysis of smoke & dust was applied to study and analyse. The results showed that the content of Cu, Ni, Co were higher in all recovery dust particles, these three heavy metals very closed to the grade of concentrates, which with a high recycling value, and it could be recycle by returning directly to the relevant process. Meanwhile, the content of As, Pb, Zn, and Cd in recovery dust of the exhaust gas, which comes from the smelting furnace, converting furnace and dilution furnace is also higher. The article also collects the recovery dust from the smelting furnace and the converting furnace in the oxygen-rich side-blown process as our primary research object, On the basis of thecomponent analysis of smoke & dust, the size characteristics and surface features analysis of smoke & dust also carried out. We could see that smoke & dust are mainly composed of a large number of micron particles of fine crystals, the content of heavy metal on the surface were lower, far less than in the bulk phase. Therefore, improving the efficiency of collecting smoke of existing devices was the key to control escaping of smoke & dust containing heavy metal.Based on the analysis of exhaust pollutant characteristics of escaping smoke &dust, a typical nickel smelting enterprise selected as the research object, its production capacity was 100,000 t/a nickel matte. Measuringpoints were set in this enterprise's workshop to study the pollution dispersion models unorganized at its downwind. Some discharge data of smoke & dust containing heavy metals obtained through on-site monitoring, then getting the heavy metal discharge source used Gaussian model by means of reverser method, And the model was validated through field tests, its had higher precision and accuracy.Heavy metals were the most important polluting components in industrial waste residue. According to the features of non-biodegradable of Heavy metal pollutants determined its long-term existence and might be a great potential threat to the environment. In this paper, waste residue in mainly pyrometallurgical smelting process of China's largest nickel producers used as the test sample, the heavy metal of Cu, Pb,Zn, As, Cr, Cd, Co, Hg, Ni was extracted totally in slag by the existing toxic leaching method of solid waste at home and abroad. The liquid-solid ratio, leaching time,extracting agent pH and oscillation mode were used as the main factor for studing in this paper, the leaching behavior of typical heavy metal ions in nickel smelting slag were discussed. The results showed that pH mixed-up by extraction agent and waste dropped when the increase of liquid to solid ratio. Concentrations of heavy metals leaching from waste residue decreased after the first increased, while the leaching total amount of heavy metals was increasing. The leaching concentration of heavy metals gradually increased with the increase of oscillation time and reached equilibrium state gradually. The leaching concentration reached a maximum at 8-12 h when the extracting agent using HAc/NaAc. PH of extracting agent was the main factor which would be affecting the leaching of heavy metals. The leaching concentration was relatively high in strong acidic medium, leaching concentration decreased gradually with the increase of pH of extracting agent, and the leaching concentration gradually stabilized to a certain extent. The differences of total heavy metal pollutants in a nickel slag sample using different leaching methods were obvious. Using HAc / NaAc buffer solution as the extraction agent which had complexation obvious impact on leaching of metal, small changes were in the acidity of the system after leaching and high amount of metal leaching. Using H2SO4/HNO3 was the extraction agent, pH of mixed solution after leaching reflected the acidity of slag, its metal leaching amount was far below theamount using the extraction agent of HAc/Na Ac, but both were higher than deionized water. There were not a certain gap in leaching total amount of nickel slag between methods of HJ/T300-2007 and TCLP. According to concentration limits of the Identification Standard of Hazardous Waste- Leaching Toxicity Identification(GB5085.3-2007), the nickel slag of test was not classified as dangerous waste, which should be belonging to general industrial solid waste of class ?.Finally, overviews of the current situation were summarized from three aspects of supervision and management of heavy metal pollution prevention and control in nickel-cobalt smelting industry. The supervision and management problems of heavy metal pollution prevention and control in nickel and cobalt smelting industry were discussed. Thus proposed suggestions of laws, regulations, policies and standards,determined the supervising subject and frequency of key nodes and pollutant.