Study On Mercury Removal In Wastewater Of Calcium Carbide Process Ploy(Vinyl Chloride) With Carrier Induced Crystallization Technology

PVC is one of the largest mercury consuming industries,and it is also one of the important sources of mercury containing waste water in China.Mercury is present in the form of Hg²⁺.Chemical precipitation method is the first choice for the treatment of mercury containing waste water by calcium carbide method PVC.However,the traditional chemical precipitation method is more cumbersome,need to coagulation,adsorption and other follow-up treatment,as well as the problem of waste water containing mercury is difficult to recycle,induced crystallization technology is its potential replacement technology.The study took cold vapor atomic absorption（CVAA）as the measurement method.Firstly,it developed total mercury and Hg²⁺measurement method study of HgS sedimentation equilibrium system,and developed influences study of Cl^-to Hg²⁺measurement meanwhile through comparison of 6 kinds of resolution methods and 6kinds of pre-processing methods.However,in a batch stirred tank reactor（BSTR）,it took Hg²⁺water distribution as the object and Na₂S·9H₂O as the precipitator.Under the best elimination conditions Hg²⁺without carrier,it compared the residual Hg²⁺concentration balancing and equilibrium time under the conditions of 8 carriers and without carrier.Additionally,this paper developed carrier absorption experiment,optimized experiment under the best carrier condition,raw water test and induction kinetics&thermodynamics studies,and took systematicξpotential measurement under different conditions.Furthermore,it took comparison with residual Hg²⁺concentration balancing of precipitation system.Finally,an initial mercury removal test on fluidized bed was carried out in the constructed fluidized bed reactor.（1）Aqua regia-microwave digestion method has high accuracy and precision,as well as short time-consuming,less reagent consumption;Under the condition of no digestion,whether the filtration had no effect on the determination of Hg²⁺;pH 7 and pH 8.5,the concentration of Cl^-≤60g/L of no influence on the determination of Hg²⁺.（2）In the experiment,8 kinds of carriers are in the process of promoting the HgS precipitation reaction,refined quartz sand,garnet,dolomite,feldspar,fluorite,also promote the precipitation reaction in kinetics;The reduction of the residual Hg²⁺concentration in the system induced by HgS was mainly caused by the induced crystallization.（3）Dolomite is the best carrier;Under the optimal conditions,the precipitation equilibrium time was 13min,and the removal rate of Hg²⁺was 99.96%;Compared with the 94.27%,97.57%under the no carrier condition,the removal rate of total mercury in 2 kinds of raw water was 99.43%,99.63%,significantly improved the effect of mercury removal.（4）Without a carrier and dolomite induced precipitation of HgS reaction rate equation are:r_n=kQ+b=k[Hg²⁺][S^2-]+b,reaction is 2 order reaction;Dolomite decreased the activation energy of HgS precipitation from 188.83 J/mol to 122.10J/mol,and significantly promoted the HgS precipitation reaction in thermodynamics.（5）To the purity of the larger or composition of the carrier,can be used pH8.5water solution,or pH8.5-HgCl₂ system is simple and easy to choose HgS crystal carrier,the law is:Zeta potential tends to be 0,HgS precipitation system balance residual Hg²⁺concentration decreases,induced crystallization effect is better.（6）In the fluidized bed reactor,the start-up time of HgS crystallization induced by quartz sand is faster,and the hydraulic retention time is much less than that of the stirred reactor.