Study On Characterization Of Lanthanum(?) Oxide Modified Silicate Minerals And Mechanism For Phosphorus Removal

Phosphorus is a limiting factor in the control of eutrophic lakes. Three silicate minerals with different physic-chemical properties, including clinoptilolite, sepiolite and kaolin were studied as phosphorus adsorbents. The optimal technological condition was established by using central composite design, which made the phosphate adsorption capacity of silicate mineral modified by lanthanum(?) oxide increased by more than eight times. The relationship between the physical and chemical characteristics of lanthanum(?) oxide modified silicate minerals and their phosphorus removal performances was elucidated. The promoting interaction and influencing mechanism between silicate mineral and lanthanum(?) oxide were analyzed. The mechanism of silicate minerals loaded with lanthanum oxide and the mechanism of phosphate adsorption were revealed.The improved hydrolytic precipitation method was involved to load silicate minerals with lanthanum oxide. The modification process can be all simulated by the Quadratic model. Among all the influencing factors, the interaction between pH value and calcination temperature was most remarkable. The best modification conditions were pH=8, solution concentration 0.3% and calcination temperature 300? for clinoptilolite; pH=8, solution concentration 0.4% and calcination temperature 200? for sepiolite; pH=8, solution concentration 0.3% and calcination temperature 300? for kaolin. Under these optimum conditions, the removal rate of 5mg/L phosphate was 99.04%,99.62%,99.49%, respectively. The phosphate adsorption capacity of silicate mineral modified by lanthanum oxide was not affected in the range of solution pH from 3 to 11. The maximum adsorption capacity of clinoptilolite modified by lanthanum oxide with improved hydrothermal synthesis method can reach to 15.06mg/g, which is much higher than the adsorption capacity of clinoptilolite prepared by Lanthanum Chloride modification process (1.75mg/g) and the mineral materials adsorbents modified with lanthanum reported in literature.Mechanisms of lanthanum(?) oxide modification were analyzed and discussed through investigating the changes of modified silicate minerals in composition, crystal structure, molecular groups and binding energy of atoms. The results showed that the modification mechanisms of clinoptilolite and sepiolite with lanthanum(?) oxide included cation exchange that Ca2+ exchanged by La3+ and electrostatic adsorption. However, the modification mechanism of kaolin by lanthanum(?) oxide was mostly based on electrostatic adsorption. La loaded on the mineral surfaces combining with aqueous-OH groups formed lanthanum hydroxide, which was roasted into lanthanum oxide. The mechanism of phosphate adsorbed by silicate mineral was revealed. The phosphate adsorption mechanism of modified clinoptilolite resulted from the formation of inner complex and surface complexation, including mainly ion exchange between-OH and PO43- to form internal complex, together with the Lewis acid-base reaction caused by La-0 chemical bond. The adsorption mechanism of modified sepiolite and kaolin was mainly a consequence by Lewis acid-base reaction caused by La-0 chemical bond.In the course of application, La in the lanthanum oxide modified silicate minerals would not be released into the water to affect water quality. The lanthanum oxide particles loaded on the surface of sepiolite and kaolin were more stable than that loaded on the surface of clinoptilolite. The optimized hydrothermal synthesis process was a green and efficient application technology for the preparation of adsorbent for phosphorous pollutants in eutrophic water, which will promote the development and application of silicate mineral carrier adsorbents.