Study On Solidification And Stabilization Of Mercury-containing Waste Slag In Xinhuang Mercury Mine

The heavy metal pollution represented by mercury in the Xinhuang mercury mine has seriously affected the local water and soil environment.Among them,the mercury residue dumps left over from history are the main sources of pollution.In this paper,bentonite,gypsum and fly ash are used as stabilizers,and the combination of cement and quicklime and fly ash is used as curing agent to carry out solidification/stabilization research of mercury-containing waste slag piles in order to control the release of pollutants from the source and Pollution of heavy metals in surrounding soil,groundwater,and Wushui River caused by mercury waste slag yards.This paper first conducts research on the occurrence characteristics of heavy metals in mercury-containing waste residues and the mechanism of heavy metal release under rainfall leaching,and then conducts solidification and stabilization experiments of mercury-containing waste residues using natural materials or industrial waste as the main material.The influencing factors of the migration ability of harmful components in the stabilized mercury-containing waste residue were studied.(1)Experiments on the occurrence characteristics and release mechanism of heavy metals containing mercury residues:The content of Hg in the waste residue was 78.8mg/kg,As content was 65mg/kg,Se content was 77.5mg/L,and other metals were low.The concentration of Hg,As,and Se in the leaching residue of the leaching solution in the leaching experiment is basically similar to the change in rainfall time.All of them have a higher concentration of heavy metals in the leaching solution from the initial stage of rainfall,and then start to decrease sharply in a short period of time.And finally remain stable.By calculating the total amount of elements in the leaching leachate within 24 hours,the results obtained are compared with the element exchangeable content of the waste residue tested by the five-step extraction method.The total amount of leached elements is far from reaching the element exchangeable State content.According to the volume of the exudate and the concentration of element leaching,the total amount of element leaching in 24 hours was calculated.According to the experimental data,it can be concluded that the lower the pH of the rainwater,the greater the leaching capacity of the elements in the waste residue.(2)The results of stabilization/curing experiments show that:The combination of 15%bentonite and 5%fly ash has a remarkable stabilizing effect on the excess elements of mercury,arsenic,and selenium in the waste residue.When cement is added separately,the compressive strength of the solidified body increases with the increase of the cement content,and the leaching concentration of heavy metals decreases;the optimal treatment conditions for the solidification/stabilization of mercury-containing waste residue:the proportion of fly ash to replace cement is 20%,The amount of quicklime as active:activator is 4%of the amount of fly ash.At this time,the leaching concentrations of heavy metals Hg and As measured in the stabilized solidified body were 0.081 mg/L and 0.862 mg/L,respectively,which met the "Control Standards for Hazardous Waste Landfill Pollution Control",and the concentration of Se element was 0.241.mg/L meets the "Dangerous Waste Identification Standard".The compressive strength of the solidified body is 1.95 MPa,which meets the requirements for safe landfill.(3)The results of dynamic leaching experiments of stabilized products show that:The rainfall leaching test was performed by simulating rainfall intensities of 100mm,200mm,and 300mm,and adjusting the pH value of the simulated rainfall to 5.5 and 7,respectively.There were four groups of experiments.The experimental results show that,as time increases,the concentration of Hg,As,and Se in the exudate as a whole is higher in the initial stage,but then decreases rapidly and finally remains stable.At the beginning of the rainfall,the mass of soluble heavy metals in the stabilized waste residue was relatively high,which resulted in a high mercury concentration in the exudate in the initial stage.By calculating the total amount of elements in the leaching leachate over a period of 24 hours,the results are compared with the element exchangeable content of the waste residue tested by the five-step extraction method.It can be found that during the leaching process,the leaching The total amount of elements is far from the exchangeable content of the elements.Therefore,in the process of water infiltration,the exchangeable components of Hg,As,and Se account for the major part of the main leaching concentration of the waste slag.The effective components of Hg,As,and Se were quickly washed away by the leachate,which caused the element concentration in the leachate exudate to rapidly decrease during this process;after the initial flushing,the remaining exchangeable components of the retained elements had a strong adsorption capacity.The Hg,As,Se active part of the slag is slowly released,resulting in the element concentration maintained at a lower concentration to remain stable.According to the volume of the exudate and the concentration of element leaching,the total amount of element leaching in 24h was calculated.According to the experimental data,it can be concluded that the lower the pH of rainwater in the case of neutral water leaching,the greater the element leaching ability in the waste residue.