| Soil leaching is one of the commonly used means of treating waste liquid arising from leaching heavy metals from soil.At present,the most important technical problem associated with this technology is the treatment of waste leachate.Due to the lack of effective heavy metal treatment techniques for the contaminated leachates that are generated,wider application of leaching technology to treat soils contaminated by heavy metals is seriously restricted.In this paper,four kinds of adsorbents and corn stalk xanthate were compared to adsorb heavy metals such as Cd2+and Pb2+.The results showed that corn stalk xanthate had better adsorbing effect for heavy metals such as Cd2+and Pb2+.The preparation technology of corn stalk xanthate was further optimized,and the adsorption characteristics of Cd 2+,Pb 2+on corn stalk xanthate were studied in terms of adsorption time,pH and temperature.The dynamic adsorption kinetics model of zein stalk xanthate adsorbent for Cd2+ and Pb2+ ions was analyzed.The dynamic adsorption curve of zein stalk xanthate adsorbent for Cd2+and Pb2+ions was studied by column simulation experiment,and its adsorption mechanism was discussed.On the basis of laboratory,pilot-scale production of corn stalk xanthate was carried out,and the practical application technology of corn stalk xanthate was analyzed.The main results are as follows.1.The adsorption characteristics of Cd2+and Pb2+ions on activated carbon,bentonite,zeolite,corn stalk and corn stalk xanthate were compared.The results showed that the adsorption capacity and rate of corn stalk xanthate were better than those of other adsorption materials.The xanthate adsorption capacity of corn stalk was the largest and the adsorption efficiency was the highest in the same time.2.The adsorption characteristics of lead and cadmium on four biomass xanthates,including starch xanthate,chitosan xanthate,wheat stalk xanthate and corn stalk xanthate,were compared.It was proved that the adsorption capacity of corn stalk xanthate was the strongest when the amount of adsorption material was 0.2g/L.The adsorption capacity of corn stalk xanthate>chitosan xanthate>wheat stalk xanthate>starch xanthate,respectively.Among them,the maximum adsorption capacity(Qm)of corn stalk xanthate for Cd2+and Pb2+ions in water was 0.170 mmol/g and 0.133 mmol/g,respectively.Quasi-second-order kinetic energy fitted well the adsorption kinetics of Cd2+?Pb2+on four xanthates,and the correlation coefficient was more than 0.9.The effects of adsorption conditions on the adsorption of Cd2+?Pb2+on corn stalk xanthate were analyzed.It was found that the optimal treatment conditions for lead and cadmium were as follows:adsorption time(>2 h),temperature(>20 C to 25 C),pH 6-8.3.The preparation technology of corn stalk xanthate.It was proved that the optimum conditions for corn stalk xanthate synthesis were NaOH concentration 20%,CS2 dosage 5 mL,xanthation time 1 h.and magnesium sulfate dosage 5%3 mL.The order of influencing factors in the preparation process is:the dosage of CS2>the xanthation time>the concentration of NaOH>the dosage of formed magnesium sulfate.The effect of corn stalk xanthate in treating waste leachate is obvious.The removal rates of Pb2+,Cd2+,Zn2+,Cr2+and Cu2+in waste leachate can reach 83.00%-99.21%.The concentration of effluent can meet the requirements of "Comprehensive Wastewater Discharge Standard GB 8978-1996".It can be used to treat waste leachate of heavy metals in soil.4.The dynamic adsorption characteristics of corn stalk xanthate on heavy metal lead were revealed.It was found that the penetration time was 96 h and the adsorption saturation time was 200 h in the column experiment with a filling height of 5 cm and a flow rate of 1 mL/min.Column adsorption results showed that corn stalk xanthate possessed the ability to adsorb heavy metal Pb2+.Column adsorption penetration and saturation depended on flow rate,column height and initial concentration.The smaller the flow rate and initial concentration,the higher the column height,the longer the penetration time and saturation time.Several penetration models can better predict the penetration curves under laboratory conditions.The faster the flow rate,the shorter the height of filling column and the larger the initial concentration,the greater the slope of the penetration curves.The experimental results of multiple adsorption cycles show that corn stalk cellulose xanthate has better adsorption performance,as well as the adsorption of actual waste leachate.The results of open column adsorption test can be applied to the treatment of waste liquor from practical leaching engineering.5.Pilot production of corn stalk xanthate was carried out.The adsorption capacity of corn stalk xanthate was monitored in pilot production.It was proved that the adsorption capacity of corn stalk xanthate was basically the same as that of laboratory pilot production,and the expected pilot production effect was achieved.The pilot-scale production process and process parameters of corn stalk xanthate were put forward.The process has the characteristics of short process flow,compact equipment configuration,small installed capacity and low energy consumption.However,the yield of corn stalk xanthate is not high,and there is still room for improvement in waste liquid reuse.6.The application of corn stalk xanthate was studied.The application in a soil heavy metal leaching project in Chenzhou,Hunan Province shows that the concentration of As,Pb2+and Cd2+is determined by sampling at the outlet and entrance of the temporary storage tank.Influent total As concentration was 0.22-0.63 mg/L,Pb2+concentration was 6.09-27.07 mg/L and Cd2+concentration was 4-13.78 mg/L.After internal circulation,the effluent concentration of total As is less than 0.02 mg/L,the Pb2+concentration is less than 0.5 mg/L,and the Cd2+concentration is less than 0.1 mg/L.The treatment effect meets the "Comprehensive Wastewater Discharge Standard GB 8978-1996".The water-saving effect is obvious. |
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