Study On The Selection Of Dissolved Solutions For Lead And Cadmium Particles Complexation

A large quantity of heavy metal-containing flue gas is produced in the metal smelting process.At present,the collection method of these exhausted particulates specified by the national standard is solid-state filter membrane sampling.But this method has many deficiencies certainly.For small size particles,they can keep an aerosol state and float for a long time.The incomplete collection of these particles can lead errors.Through the analysis of the composition of metal ores,it can be seen that basically all the metal ores contain many kinds of heavy metals,especially lead,cadmium and their compounds.In this paper,the dissolution rate of ultrafine powders of lead,cadmium and their compounds in complexing agents is studied.Based on the dissolution rate of heavy metals in the solution,kinds of complexing agents were selected.The dissolution and absorption of metals and their mixed components were studied.The application of complexometry method in the absorption of heavy metal smoke was analyzed.The main results are as follows:(1)Side reactions would occur during the complexation of heavy metal ions with complexing agents.The degree of the binding of metal ions to hydroxyl,and the degree of complexation of ligand with proton at different pH were calculated.According to the complexation equilibrium constants of the complexing agents and metal ions,the conditional stability constants were obtained.The results showed that,the complexing agent could be considered as a adsorbent for heavy metal ions when the the stability constant was more than 6 in the complexation process.(2)For lead,two complexing agents were selected: HEDTA and citric acid.The optimal dissolution condition of HEDTA was pH of 5,HEDTA concentration of 0.1 mol/L,reaction time of 50 min,temperature of 30 °C.The dissolution rate could reach 25.31% under the optimal condition;The optimal dissolution condition of citric acid was p H of 3,citric acid concentration of 0.15 mol/L,reaction time of 40 min,temperature of 50 °C.And the dissolution rate could reach 25.31% under this condition.The best complexing agent of lead oxide was EDTA.And the optimal dissolution condition was pH 5,EDTA concentration of 0.2 mol/L,dissolution time of 50 min,and reaction temperature of 50°C.Under this condition,The dissolution rate of lead oxide could reach 96.33%.The optimal complexing agent of lead sulfide was EDTA.The best dissolution co ndition was pH of 5,EDTA concentration of 0.2 mol/L,and reaction time of 40 min,reaction temperature of 60°C.The dissolution rate of lead sulfide could reach 43.95% under this condition.(3)The best complexing agent for the three-component mixture of lead,lead sulfide,and lead oxide was citric acid.The optimal dissolution co nditions was p H of 4,citric acid concentration of 0.15 mol/L,and reaction time of 50 min,reaction temperature of 50°C,the dissolution rate of citric acid could reach 69.52% under this condition.The optimal solution for the dissolution and dissolution o f lead oxide and lead sulfide was HEDTA.The optimal dissolution condition was pH of 3,HEDTA concentration of 0.1mol/L,the dissolution,and reaction time of 50 min,reaction temperature of 50°C.The dissolution rate of HEDTA could reach 93.62% under this condition.(4)The best dissolving solution of cadmium oxide was EDTA.The optimal dissolution condition was pH of 5,EDTA concentration of 0.1 mol/L,and reaction time of 50 min,reaction temperature of 60°C,and the maximum dissolution rate of EDTA could reach 97.64 % under this condition.The best dissolving solution of cadmium sulfide is citric acid.The optimum dissolution condition was p H of 4,EDTA concentration of 0.15mol/L,dissolution time was 50 min,reaction temperature of 50°C.The maximum dissolution rate of EDTA could reach 38.83% under this condition.(5)The best dissolving solution of cadmium oxide and cadmium sulfide was EDTA.The optimal dissolution condition was pH of 5,temperature of 50°C,EDTA concentration of 0.1mol/L,and reaction time of 50 min.The maxmuim dissolution rate could reach 90.52%.(6)The effects of four factors on pH,temperature,time,and solution concentration in the dissolution tests of metals and their compounds are: pH> solution concentration> dissolution time> reaction temperature.Comprehensive analysis of heavy metals in the complex dissolved solution has a high efficiency of dissolution,to make up for the lack of existing sampling methods,can achieve the maximum particle size of the smaller particle capture,and liquid absorption method is simple and convenient operation,with Broad application prospects.