Experiment On Solidification Of Tailings Slag By Calcium Carbonate Precipitation Induced By Microorganism

The tailings treatment in arid areas is faced with the disadvantages of water resources shortage,soil barren,salinization and relative lack of plant resources,which hinders the ecological recovery process of the region to a great extent.It is of great scientific significance and practical value to study the comprehensive treatment of tailings and ecological restoration and solidification technology to guide the coordination of mine development and utilization and ecological environment protection in arid areas.Microbial induced calcium carbonate precipitationis a kind of biomineralization process widely existing in nature.It has simple mechanism,fast and high efficiency,and good environmental tolerance.It has become a hot research hotspot of heavy metal solidification and wind erosion prevention in mining area.The main research content of this paper is to use lysiniacillus fusiformis to solidify tailings soil with different particle sizes.The morphology of tailings is observed by SEM,and the phase analysis is carried out by X-ray diffraction.The wind tunnel test and pressure test without side limit verify its anti wind erosion capability;The influence of micp on the physical and chemical properties and heavy metal content of tailings soil with different particle sizes was also studied.The main conclusions are as follows(1)The experiment uses the fermentation liquid of OD600=2,the cement liquid prepared by urea and calcium chloride lmol/l,and conducts different particle size solidification experiments on the sample of 910cm2 tailings soil,including K1(<5mm),medium particle K2(5-15mm),coarse particle K3(>15mm),the results show that it is feasible to cure tailings soil by micp technology.The results of XRD and SEM show that the micp treated tailings produce calcium carbonate crystal with cementation and solidification ability.The unconfined compressive strength of tailings soil with different particle sizes after micp treatment was enhanced.After adding fine particles(<5mm),the shear strength was 1.25 times of that of uncured,and the maximum value reached 1393kpa;The medium particles(5-15mm)are 2.21 times of uncured,and the maximum value reaches 2371 kpa;The coarse particle K3(>15mm)is 1.40 times of that without micp,and the maximum value reaches 1909kpa.The anti wind erosion ability of tailings soil was improved by adding micp.The solidification rate of fine particles was 98%-99%at 8-22m/s wind speed;The solidification rate of the medium particles is 43%-81%;The curing rate of coarse particles is 38%-87%.(2)The urease activity and nh4+content of soil of micp were significantly increased(P<0.05),from 34.47u/g-49.15u/g and 0 before curing to 59.19u/g-64.14 u/g,84.43mg/l-116.92 mg/1,respectively,53.33g/kg and 51.33g/kg(P<0.05).The nutrient content(total carbon content,total nitrogen content,total potassium content),soil enzyme activity(catalase,Sucrose Enzyme)and conductivity value of micp increased compared with those before the tailings were solidified;The pH and total salt content of tailings soil decreased significantly(P<0.05),from 9.03-9.38,14.18g/kg-22.86g/kg before the uncured to 8.62-8.9 and 14.18-14.3g/kg.(3)Except for the elements Ni,the total contents of CD,as,Cu,Pb,Cr and Hg heavy metal ions in tailings soil exceed the national background value.After micp treatment,the contents of Cr,Cu,Ni,Hg and Cr,Cu,CD and PD in the coarse particles all decrease.The content of heavy metals can be reduced by adding micp.The leaching test shows that the release of the same metal in different particle sizes is different,and the metal stability of Ni,Pb and Cr treated by micp is higher;The release of as,CD and Hg increased,and the metal migrated in neutral or alkaline conditions.The size of soil particles has a great influence on heavy metal adsorption,and the ability of heavy metals adsorption in coarse tailings soil is stronger.After adding micp,the content of heavy metal weak acid in K3+m decreased,and the residual content increased.The curing rate of CD,Pb,Ni,Cr and Cu weak acid was 43.86%,41.76%,29.23%,23.20%and 5.00%respectively.From the perspective of the effectiveness of heavy metals to the environment,Cu has the highest harm to environment and biology in tailings,followed by CD,and Ni is the most stable and the least harmful.The results show that the bauxite soil can be solidified by Bacillus lysine.The cemented tailings produce carbonation in the microstructureThe content of residue state increased significantly,and the soluble content decreased significantly.