Experimental Study On Cd(â…¡) Polluted Groundwater Repairing With PHospHorus-containing Substances

For the purpose of "p HospHorus-containing substances passivation repairing groundwater polluted by heavy metals", this paper has done a thorough research on the effect and mechanism of pHospHorus on heavy metal pollution of groundwater. By batch and column experiments, the effect and main influencing factors of p HospHorus-containing substances passivation repairing groundwater polluted by heavy metals was studied. The feasibility and effectiveness of PRB repairing cadmium contamination groundwater with pHospHorus-containing substances was discussed and the mechanism was studied.The conclusions were as follows:（1）pHospHorus-containing substances was an effective adsorbent to remove metal ions from an aqueous solution, and has a good adsorption effect on Cd²⁺. The data regression of apatite and tricalcium pHosp Hate adsorption kinetics on Cd²⁺was made, showing that the adsorption kinetics consistent with Lagergren pseudo-second reaction rate model. Apatite and tricalcium pHosp Hate adsorption behavior on Cd²⁺ can better fit Freudlich model and Langmuir model, the analysis result of the two models was quite consistent. However, tricalcium pHospHate and apatite were expensive, so activated carbon in the next experiment was added.（2）The main factors affecting adsorption effect of apatite, tricalcium pHospHate and activated carbon on Cd²⁺ were pH, ionic strength, adsorbent dosage, mixing different sorbents proportion. When pH = 7, the adsorbent had a best adsorption effect on Cd²⁺, the adsorption capacity of the adsorbent was weakened while increasing the ionic strength. The studies showed that the optimum adsorbent amount of apatite, tricalcium pHospHate, activated carbon were 0.02 g, 0.04 g, 0.08 g. The optimum mixing ratio of HAP + activated carbon, Ca3（PO4）2 + activated carbon were 1: 6, 1: 8.（3）The desorption rate of Cd²⁺ decreased with desorption time increasing, and then stabilize. The data regression of Cd²⁺ desorption kinetics with apatite and tricalcium pHospHate showing that the adsorption kinetics was consistent with Lagergren pseudo-second reaction rate model. The cadmium desorption rate and pH presents negative correlation, the cadmium desorption rate and ionic strength presented positive correlation. It could be seen from the results that apatite, tricalcium pHospHate,activated carbon all have a good adsorption on Cd²⁺, and limited desorption capacity.（4）Experiments showed that, if the effluent concentration can reach national drinking waterstandards of 0.01 mg / L to meet the needs of removing, considering removal efficiency and saving raw materials costs, the best ratio of quartz sand + HAP + activated carbon was 10: 1: 6, and the best ratio of quartz sand + Ca3（PO4）2 + activated carbon was 10: 1: 8. It fully proved the feasibility and effectiveness to PRB repair cadmium polluted groundwater with apatite, calcium pHosp Hate.