Activation Of Phosphate Rock And Removal Of Heavy Metals By Activated Phosphate Rock

The deficiency of soil phosphorus is very serious in China,and this phenomenon is bad for the agriculture production.Low molecular weight organic acids（LMWOAs）are widely existed in soil and can be used as a kind of activator to increase the available phosphorus content.In addition,there are a large number of phosphate-solubilizing microorganisms in soil,which can improve the effect of phosphorus release through the secretion of organic acids.With the rapid development of industry and agriculture in China,the pollution of heavy metals in the environment has become a general trend and has attracted more and more attention.Phosphate rock resources are abundant in China,but most of them are mid-low grade.It has some advantages of wide range of sources and low prices in the treatment of heavy metals pollution.In order to provide theoretical basis and technical support for the scientific utilization of mid-low grade phosphate rock and the management of heavy metal pollution,the activation of mid-low grade phosphate rock by low molecular weight organic acids and the utilization of the PR in heavy metals removal in water were studied in this paper.The activation effect on PR by oxalic acid and tartaric acid under different reaction conditions was studied,and the immobilization effect on lead and cadmium in water of the PR and activated PR was explored.In addition,the remove of lead and cadmium ions by PR combined with soil microbes in water was also studied.The results are as follows:1.Activation and phosphorus releasing kinetics of mid-low grade PR by LMWOAsThe results of the activation of PR using formic acid,acetic acid,lactic acid,salicylic acid,pyruvic acid,citric acid,oxalic acid and tartaric acid showed that these organic acids have different degrees of activation ability of PR at certain concentration.Under the condition of acid concentration of 40 mmol/L,oxalic acid has the best effect on the activation of PR,followed by tartaric acid.The activation efficiencies of oxalic acid and tartaric acid on PR were investigated based on different acid concentration,activation time,ratios of liquid-solid（volume of organic acid solution to amss of PR）,reaction temperature and initial pH of solution.The results showed that the optimum conditions of activation of PR by oxalic acid were as follows:acid concentration 20 mmol/L,activated time 4 d,temperature 20℃,solution initial pH 2,liquid-solid ratio 100:1（mL:g）.The optimum conditions of activation of PR by tartaric acid were as follows:acid concentration 60 mmol/L,activated time 24h,temperature 10℃,solution initial pH 2,liquid-solid ratio 50:1（m L:g）.The processes of PR dissolution were described with different kinetics equations.The results indicated that the first-order equation would be suitable for the description the whole process of oxalic acid activated PR and the initial process of tartaric acid on phosphorus release.2.Exploration of the removal of Pb²⁺and Cd²⁺by PR and activated PRThe removal of Pb²⁺and Cd²⁺in water using PR and activated PR by oxalic acid and tartaric acid were studied.The effects of PR and activated PR on the adsorption of Pb²⁺and Cd²⁺were investigated based on different initial concentration of heavy metal ions,adsorption time,initial pH of solution and dosage of adsorbent,and the relevant adsorption dynamics of Pb²⁺and Cd²⁺were analyzed.The results showed that the PR activated by oxalic acid has no positive influence on the adsorption of Pb²⁺,but enhanced the adsorption of Cd²⁺.Tartaric acid activated PR had an inhibitory effect on the removal of both Pb²⁺and Cd²⁺.In addition,the adsorption isotherm of PR on Pb²⁺and Cd²⁺were in accordance with Langmuir,while adsorption isotherm of activated PR on Cd²⁺were more consistent with Freundlich.The adsorption process of PR and activated PR on Pb²⁺and Cd²⁺were dominated by chemical adsorption,and were associated with pseudo-second order kinetic model.3.The removal of Pb²⁺and Cd²⁺by microorganism combined with PRFour strains resistant to Pb²⁺and Cd²⁺were isolated,and among them,Aspergillus sp.and Mucor sp.were resistant to Pb²⁺,Penicillium sp.and Achromobacter sp.showed resistance to Cd²⁺.The effects of single strains and mixed strains on the removal of Pb²⁺and Cd²⁺in water were studied,and the cooperative adsorption of Pb²⁺and Cd²⁺by adding PR with microorganisms were carried out.The results indicated that Aspergillus sp.has a stronger ability to adsorb Pb²⁺than Mucor sp.,and Penicillium sp.which compared with Achromobacter sp.has greater adsorption ability on Cd²⁺.The removal effect on Pb²⁺and Cd²⁺by mixed strains was more effective compared to the single strain.Using microorganism combined PR to remove Pb²⁺and Cd²⁺in water,PR has a significant effect on the adsorption of Pb²⁺and Cd²⁺by a single strain,while the addition of PR can accelerate the process of adsorption.