Risk Assessment Of Heavy Metals In Dust Reduction During Co-processing Of Metal Tailings And Smelting Slag In Cement Kilns

Lead-zinc tailings and copper smelting slag are metal wastes left over from the extraction of valuable resources in metal minerals by industrial and mining enterprises.In order to avoid improper placement of wastes from harming the environment,using cement kilns for coprocessing is commonly harmlessness and resource-based disposal method in China.However,a large amount of heavy metals will spread to the plant area or settle into the surrounding soil environment along with the fugitive emissions in all stages of production in a cement plant,which will adversely affect the health of the workers in the plant and the surrounding environment.In this study,under the conditions of mixing raw materials with lead-zinc tailings in different proportions,the dust fall in each production link in the cement plant was collected,and the farmland soil on the downwind side of the plant was collected.The contents of Hg,As,Cr,Cd,Cu,Pb,Ni,and Zn in the samples were tested.Use the RAGS risk assessment model to assess the possible health risks of the samples in the factory.In addition,four ecological pollution index methods are used to analyze the environmental pollution that may be caused by soil heavy metals.The results are as follows:(1)In the cement plant,the contents of various heavy metals in lead-zinc tailings and copper smelting slag are higher than those in the dust fall of other production sections,and the high content of As in the lead-zinc tailings and copper smelting slag shows a high hazard index by ingestion route,which exceed 80% of the total non-carcinogenic hazards of the two raw material storage yards,is the main hazard factor.When using the population parameters in the "Chinese Population Exposure Parameters Manual(Adult Volume)",the HIAs in the lead-zinc tailings yard and the copper smelting slag yard were 7.19 and 4.96,respectively.The total carcinogenic risk value of heavy metals in the lead-zinc tailings yard is 1.13E-06.When using the actual exposure parameters investigated,the HIAs in the two storage yards are 5.22 and3.60 respectively,and the total carcinogenic risk of heavy metals in the lead-zinc tailings yard is 2.45E-07.It can be seen that because some of the actual parameters are smaller than the exposure parameters in the "Chinese Population Exposure Parameters Manual(Adult Volume)",the actual risk results are smaller than the results of using the exposure parameters in the "Chinese Population Exposure Parameters Manual(Adult Volume)".In addition,the heavy metals in the two storage yards have non-carcinogenic hazards that cannot be ignored to the workers.(2)The various equipment workshops and material storage yards in the factory showed different amounts of dust fall and changing trends during the three sampling periods.The content of heavy metals in the dust fall is also different from each other.In the preparation stage of the finished product,the dust fall of the cement roller press workshop and the cement warehouse is affected by the mixed material of lead-zinc tailings and copper smelting slag.The content of heavy metals in the dust fall in the two place is higher than other production sections.Using the "Chinese Population Exposure Parameter Manual(Adult Volume)" to carry out risk assessment of heavy metals in dust reduction,it was found that the total non-carcinogenic hazard value of the cement roller press workshop under three different lead-zinc tailings premixing ratios exceeded 1,they are 1.34,1.29,1.53,respectively.The HIT value of dust reduction in the cement warehouse workshop reaches 2.22 when the pre-mixing ratio of lead-zinc tailings is 1.5%wt.The HIT values of other materials,coal stockyards and equipment workshops are all less than 1,and there is no non-carcinogenic health hazard.When the actual parameters are used for risk assessment,under the three pre-mixing ratios of lead-zinc tailings,the HIT of heavy metals in the cement roller press workshop is 9.71E-01,9.32E-01,and 1.11.It can be seen that when the pre-mixing ratio of lead-zinc tailings is 1.5%wt.,the workshop only has HIT exceeds 1,and there is a hazard.The main hazards here are still As,Pb,and Cu.When the premixing ratio of lead-zinc tailings is 1.5% wt.,the HIT of heavy metals in the dust reduction of the cement warehouse is 1.61,and the HI value of As is 1.31,which is the main hazard factor here.There is no harm in other workshops.When using the two parameters,the total carcinogenic risk TCR value of each place does not exceed the risk threshold of 10-6,and there is no harm.(3)The content of heavy metals in the soil outside the plant showed that the average concentrations of Pb,Cu,and Hg all exceeded the background value of the local soil environment in Hechi,and there was a certain degree of accumulation in the soil in the study area.The results of single factor pollution index and Nemeiro pollution index show that the Pi value of Hg in the soil in this area is 4.05,which is a heavy pollution level,Cu and Pb are light pollution levels,and other heavy metal elements are at a non-polluting level.Under the influence of Hg,the overall Nemeiro pollution index PN value is 3.00,which is a moderate pollution level.The results of the local cumulative pollution index show that the average Igeo value of Cd is 4.19,the average Igeo value of heavy pollution and Hg is 2.17,the average Igeo value of medium-intensity pollution,and the average Igeo value of Pb and Cu is between 0 and1.-Moderate pollution,the average Igeo value of other heavy metals is less than 0,which is non-polluting.The results of the potential ecological risk index show that the potential ecological risk index of Hg in the soil in the area is 161.98,which is a very strong level of hazard.The remaining heavy metals are at a slight potential ecological risk level.The potential ecological risk index of the soil in the entire region is 213.72,which is a moderate hazard.Level,and the contribution rate of Hg reaches 75.79%.Different evaluation methods have shown the Hg pollution in the soil,and relevant measures need to be taken after further analysis of the Hg source and pollution degree.As the main hazard factor in the plant,As is solidified in the cement production process due to its non-volatility,and is not emitted with smoke and dust,so it does not pollute the soil outside the plant.