Research On Heavy Metal Cementation And Soil Improvement By Microbially Induced Mineralization Technology

Microbially induced mineralization technology(MIM)is a new application of biomineralization.The basic principle of the technology is hydrolyzing urea to generate carbonate ions and hydroxyl ions by the producing urease bacteira.The ions can react with the free metal ions to form precipitation,which can reduce the heavy metal pollution,cement soil particle and improve the mechanical properties.It seems to be a new method to treat the tailing sand.The work has done and the achievements include:1.The paper uses biochemical analysis method to find the relationship between enzyme activity of the Sporosarcina pasteurii and the preservation time at normal temperature.The enzyme activity goes up firstly then goes down with the time under the normal temperature,and the toppest point appears at 54h-66 h.However,the enzyme activity in the supernatant changes little over time,increased slightly.Also the effect of the heavy metal ions concentration on the enzyme activity is explored,and the results show that the heavy metal ions(Pb,Cd,Zn,Cu,Co)have inhibition on enzyme activity,and different heavy metal ions have different degrees.2.MIM technology is used to treat the solution containing heavy meal ions and to find the different effects of different heavy meal ions.The results show that under the experimental condition,the immobilization rate is ranked as Pb>Cd>Zn>Cu>Co,especially for Pb and Cd,whose largest immobilization rate can reach 99.37% and95.52% separately.In addition,the urea concentration in the nutrient can affect the immobilization rate of the heavy metals too.3.MIM technology is used to treat the tailing sand.Different MIM programs are carried out on two different kinds of tailing sand.And after MIM treatment,both the P-wave velocity and the unixial compressive strength of the two kinds of tailings increased.However,there is a slight difference between them.The improvement of the mechanical properties of sandy tailing is better than that of clayey tailing.The P-wave velocity of the sand treated with extra Ca2+ is up to 2026m/s,and the UCS can reach6.86 MPa.Besides,MIM technology can reduce the dissolution of some heavy metals in the tailing.Compared to the concentration in the tailing without MIM treatment,Mn is reduced by 45%,and Mo is reduced about 98%.4.The influence factors of the calcium carbonate's crystal shape(including environment,calcium source and the concentration of magnesium ions)are discussed.The results show that when the calcium source is calcium acetate in the solution environment,no matter introducing magnesium ions or not,there is no aragonite in the action product.But when the calcium source is calcium acetate in the glass beads,there is needle-like aragonite..The extra little introduction of magnesium ions will contribute to the formation of aragonite and the improvement of UCS of the glass bead column.When the calcium source is calcium chloride in the glass beads,no matter introducing magnesium ions or not,there is no aragonite.