Study On Depth Chemical Modification Of Diatomite And The Adsorption Properties On Cd²⁺、Pb²⁺

Diatomite is a nature soil mineral with many excellent advantages, such as high adsorption ability, wide source and reasonable price, so it is widely used to adsorb heavy metal ions. But its adsorption ability is limited by some physical and chemical structure. In order to improve its physicochemical properties and application level, it is necessary to do research in modification of diatomite. Pillared agent, as an advanced modification technology, is a new tool which can improve the lamellar spacing, stability, special surface area and surface activity of layered materials. It is of importance to modify diatomite with pillared agent. In this article, we adopt poly-hydroxyl aluminum as pillared agent to do this chemical modification experiment. After adsorbing Pb2+, Cd2with diatomite and modified diatomite respectively, modification mechanism and technological conditions are studied in this paper. Conclusions can be got as following:(1) Static adsorption experiments reveal that the adsorption ability of diatomite depends closely upon initial concentration of heavy metal ion, the dosage of diatomite, temperature, and adsorption time. Diatomite adsorption amount is increased with the increase of initial concentration of heavy metal ion, adsorption time and pH. While the adsorption amount increase at first and then reduce with the ascension of temperature and the dosage of diatomite. The importance of adsorption factors are shown as follows: initial concentration of heavy metal ion> pH> the dosage of diatomite>temperature> adsorption time.(2) The experiment of optimum modification conditions reveals that when the initial concentration of Cd2+is1500mg/L, the dosage of diatomite is50g/L, pH is8, temperature is25℃and adsorption time is120min, both the adsorption of Cd2+and Pb2+get the optimum condition.(3) Pillared modification experiments reveal:when to adsorb Cd2+, the optimum modified conditions of diatomite is that the concentration of pillared liquid is0.2mol/L, molar ratio of [Al]/soil islOmmol/g, reaction temperature is60℃, reaction time is120min, activation temperature is105℃and activation time is16h. When to adsorb Pb2+, the optimum modified conditions of diatomite is that the concentration of pillared liquid is0.1mol/L, molar ratio of [Al]/soil islOmmol/g, reaction temperature is60℃, reaction time is120min, activation temperature is105℃and activation time is16h.(4) Through comparing the adsorption performance before and after modification, the study found that: when to adsorb Cd2+, the saturation absorptive capacity of diatomite is6.9mg/g and the removal rate is34.5%, while the saturation absorptive capacity of modified diatomite is10.05mg/g and the removal rate is50.3%, so the saturation absorptive capacity and removal rate of modified diatomite is greater than diatomite. When to adsorb Pb2+, the saturation absorptive capacity of diatomite is10.39mg/g and the removal rate is67.9%, while the saturation absorptive capacity of modified diatomite is13.62mg/g and the removal rate is67.9%, so the saturation absorptive capacity and removal rate of modified diatomite is greater than diatomite.(5) SEM experiments reveal that: compared with original diatomite, modified diatomite has more smooth surface and less impurity. In order to provide more adsorption sites for Cd2+and Pb2+, the poly-hydroxyl aluminum particles enter into layers of diatomite and then exchange with exchangeable cations. That is why the adsorption ability of diatomite is improved after modifying with poly-hydroxyl aluminum.