Study On The Precipitation Regularity Of As From Tailings Solidified Backfill Of A Gold Mine In Guizhou

With the progress of society and the deepening of the concept of sustainable development,China’s non-ferrous metal mines are developing in the direction of green mining,and the state strictly prohibits the construction of new mine tailings stockpiles.To solve this problem,most mines use the fill-and-fill method and backfill the pit with tailings solidification.After the tailings solidify and fill into the goaf area,it will be in a relatively closed mine water infiltration environment for a long time,and the tailings solidifier and the mine water will produce complex water-rock interaction,which may change the physical and mechanical properties of the tailing solid,and the toxic and harmful elements precipitated in the tailing solidify will migrate and spread within the floor of the goaf,which will produce a potential risk of groundwater environmental pollution.In order to study the precipitation of As in the solidified backfill of gold mine tailings,this paper took a gold mining area in southwest Guizhou as the research area,and prepared and maintained the solidified body with a tailings crushed stone ratio of3:2,gray sand ratio of 1:6 and a filling concentration of 75% through field investigation,field testing and sampling.The solid-liquid ratio was set to 1:10,indoor experiments such as static immersion,dynamic scouring,compressive strength and other indoor experiments were used,and mathematical statistics method,single-factor pollution index method,Nemerow comprehensive pollution index method and other analysis methods were used to systematically study the precipitation law of gold mine tailings solidified backfill AS,and a mathematical model of As element precipitation was established.The following main conclusions were drawn:(1)According to the physical and chemical properties of 14 water sample points around the mining area,the characteristics of the water quality status of the study area were evaluated: the As content in the mining area was higher than that in the surrounding waters,and the surface water was higher than that in groundwater.The As content in the water in the interior of the mining area and in the sulphur plant ditch area was 1255～44400 μg/L,which exceeded the surface water/groundwater class III.water index by 125～4440 times;The As content in the water of the Zhilou River downstream of the mining area was 2.31～5.72 μg/L,which did not exceed the surface water/groundwater class III.water index.By comparing the spatial distribution characteristics of arsenic content in soil and water samples,it was found that the spatial distribution characteristics of arsenic content in the two were basically the same,both had higher arsenic content in the mining area,while the arsenic content in the surrounding area was significantly reduced.(2)Through the static immersion experiment on the tailings and solidified backfill,the As,p H,Ec and TDS values in the solution were measured and analyzed,and the precipitation law of As in the soaking solution of the tailings and solidified backfill gradually increased with time.When the maximum value is reached,it gradually decreases,and finally gradually stabilizes.The As precipitated by the tailings is much larger than that precipitated in the solidified backfill,indicating that the tailings can consolidate the As elements after solidification.As has significant correlation with p H,TDS and Ec.According to the groundwater quality standard,whether it is tailings or solidified backfill,when the soaking reaches stability,the content of As elements in the immersion solution exceeds the groundwater quality class III.standard,and the risk of pollution is greater.(3)Through the dynamic flushing experiment of tailings and solidified backfill,the As,p H,Ec and TDS values in the solution were measured and analyzed,and the precipitation law of As in the washout liquid of the tailings and solidified backfill was the same as that of the static immersion experiment.However,the amount of precipitation when the As precipitation reaches stability is different,and the static immersion precipitation amount is greater than the dynamic erosion precipitation.According to the groundwater quality standard,it can be seen that whether it is tailings or solidified backfill,when the flushing reaches stability,the content of As elements in the flushing fluid exceeds the groundwater quality class III.standard,and the risk of pollution is greater.(4)The changes of the compressive strength of the cured backfill under different curing age conditions were analyzed and it was concluded that the longer the curing period,the greater the compressive strength value of the cured backfill.Under the same curing age conditions,the effect of static immersion on the compressive strength of the cured backfill was significantly less than the effect of dynamic erosion on the compressive strength of the solidified body.(5)The precipitation mathematical model of As was established and verified.A variety of mathematical equations were used to fit the concentration process of As precipitation in the tailings and solidifiers with time,and the correlation coefficient R2 was used to judge the advantages and disadvantages of the model.It was determined that the y=a+bcx function model was the precipitation model of As,and the experimental value and the calculated value were compared and analyzed to show that the relative error between the two was small,indicating that the established model could be applied to the precipitation prediction of As in mining areas.