Study On The Adsorption Of Lead And Cadmium Onto Natural Surface Coatings, Sediments And Their Major Components By Titration Method

Investigation on the sorption rule of heavy metal onto nature surface coatings and sediments is helpful to analysis and forecast the transference rule of heavy metal in nature water, for they both posess distinct sorption with heavy metal.Selective extraction was applied to separate the major components of nature surface coatings and sediments. Acid-base titration method was carried on studing the proton-binding sites characteristic of nature surface coatings, sediments and their major components, according to linear programming with nonlinear least squares fitting. Analysis the characteristics of surface proton-binding sites of nature surface coatings, sediments and their major components, also the relations of the components points and nature surface coatings and sediments points.Nature surface coatings and sediments were bring up and collected in jingyue pool.Founding the volume and dry weight relation to mesure the nature surface coatings and sediments. Choosing the extraction method by dong to extract nature surface coatings, and choose the improving method to extract sediments. Then quanlitified the TOC, iron oxides and manganese oxides in nature surface coatings and sediments.Take acid-base titration method on fore-and-aft extraction nature surface coatings and sediments. Each acidified solution was titrated with a 0.05 mol/L CO2-free NaOH solution in an anaerobic chamber. Titration was carried out by increasing the pH stepwise at 0.2 increments. The charge excess in the solution at each step was calculated from the concentration of NaOH and the pH value, the titration range is from 3 to 11. Each sample solution was titrated in duplicate.The data of charge excess versus pH were then analyzed by the linear programming method, as discussed in the following section. Fitting the charge excess versus pKa with nonlinear least squares fitting, figure out the surface binding site pKa and density.The test result educed that both nature surface coatings and sediments have four surface proton-binding sites, but the pKa of them are various for the different growing background. The unit mass density of points on nature surface coatings is higher than that on sediments; also each density of point is different. So the components in nature surface coatings and in sediments are various.Analysis the characteristics of heavy metal binding on nature surface coatings and sediments in various pH, applied adsorption thermodynamics method, according to surface proton-binding character. Take adsorption thermodynamics method in choosen pH of various metal concentions and in choosen metal concentions of various pH. The adsorption background is 150mL 0.1 mol/L KNO3, with mesurable Pb(NO3)2, Cd(NO3)2 in to form various concentions. Put measurable sorbents in background solution, used HNO3 and NaOH to adjusted pH,shake the adsorption system for 24 h. The equilibrium solution should filtered by 0.45μm decline hole membrane, that was extract in 25ml 15%HNO3 shaking 24h. Then observed Pb and Cd adsorption were analyzed by FAAS. That was found adsorption of lead and cadmium on nature surface coatings is higher than on sediments from adsorption data, for the density of points on nature surface coatings are higher than sediments, and the ability of binding ion is stronger. Nature surface coatings and sediments adosopt lead higher than cadium in low pH, and when manganese oxides are extracted the adsorption decrese, so the point 1 in manganese oxides is important to adsorption in low pH. The adsorption rule of iron oxides and organic matters are the same to increase with pH rise. The binding site 2 gives the leading effects to the most adsorption of lead after pH6. The binding site 2 and 3 give the leading effects to the most adsorption of cadmium after pH7. Take the same way to analysis the the adsorption rule of iron oxides and organic matters in sediments. The binding site 2 gives the leading effects to the most adsorption of lead after pH6.5. The point 2 and 3 give the leading effects to the most adsorption of cadmium after pH7.5.The test haves significance for understanding the mechanism of heavy metal and nature surface coatings and sediments, moreover help to analysis and forecast the transference rule of heavy metal in nature water.