The Preparation And Performance Research Of Rare Earth-modified Ion Exchange Resin As Adsorbent For Arsenic

Arsenic is a metalloid element, presenting widespread throughout the earth's crust in three allotropic forms of dark brown, yellow brown and gray. It can exist in the form of organic and inorganic chemicals with the pentavalent and trivalent valence state. Although the arsenic is trace elements which were necessary for human body, the excessive ingestion of it will cause a series of problems regarding pernicious effects. The arsenic has been designated as a class I carcinogen in environmental pollutants.Water pollutions caused by arsenic, which can occur due to both natural reasons and anthropogenic activity, have drawn much attention in recent years. It leads to higher requirements of arsenic pollution control in water due to successive occurrences of severe arsenic pollution accidents. Several methods and technologies, such as precipitation, ion-exchange, membrane, electrolysis, oxidation, adsorption and biochemistry have been developed for arsenic removal from water. Most of these methods have low removal efficiency for arsenite.The rare earth element widely used in the fields of metallurgy, machine, energy and environment protection. Hydrates and salts of rare earth oxides have a very high adsorbing capacity for ions. There have been considerable works reported on the adsorption of harm ions in water by Lanthanum, Cerium or other rare earth elements compounds. The problems of using rare earth elements in water treatment are hard to recovery and high cost. Some studies successfully loaded the rare earth on the operational material as absorbent in the field of water treatment and the problem is the absorbent has poor stability. The ion exchange resin, which has the function of ionexchange, dewatering, discoloration, adsorption and catalysis, has been widely applied in in many water treatment processes.In the present study, the lanthanum and cerium modified ion exchange resin has been prepared by impregnation of lanthanum and cerium into ion exchange resin beads using ion exchange reaction and studied as possible adsorbents for arsenic from aqueous solutions. Research finds that the anion exchange resin can't be modified by lanthanum and cerium. The cation exchange resin, which had no affinity to anions, can absorb the arsenate and arsenite anion in water after modified by the lanthanum and cerium. Both the adsorption capacity of As(Ⅴ) and As(Ⅲ) onto the Cerium modified cation exchange resin are obviously higher than onto the the lanthanum modified resin. The Cerium modified cation exchange resin, prepared by Cerium and cation exchange resin in a ratio of 0.217:1 at room temperature, can be used as an absorbent for arsenic remove from water.The Scanning Electron Microscope analysis for the Cerium modified 001×7 resin indicated that the Cerium compounds were successfully bonded to the resin. The X-ray Photoelectron Spectroscopy(XPS) survey results revealed that the tetravalent valence was the main existing form of Cerium in Cerium modified resin. The modified resin was confirmed to be a good adsorbent of arsenic ions and the adsorption capacity for As(Ⅲ) is higher than for As(Ⅴ).The adsorption kinetics of As(Ⅴ) and As(Ⅲ) obey a pseudo second-order kinetic model. The adsorption of As(Ⅴ) followed the Freundlich adsorption isotherm model and the adsorption isotherm data for As(Ⅲ) fitted well to the Langmuir equation model respectively. Both the adsorption of As(Ⅴ) and As(Ⅲ) were found pH sensitive and the optimum pH. was found to be 5-6. Except for phosphate ion, the coexistent ions, such as nitrate, chlorate, sulphate, carbonate, potassium, magnesium, calcium and iron ion, showed no remarkable effect on As(Ⅴ) and As(Ⅲ) adsorption.The desorption of As(Ⅴ) and As(Ⅲ) ions absorbed on the Cerium modified 001×7 resin can be carried out by 0.5 mol·L-1 sodium hydroxide solution. The desorption efficiency of As(Ⅴ) by sodium hydroxide solution is better than As(Ⅲ) and the optimal desorption time was 3 hours for both two ions. The adsorption capacity of Cerium modified resin for As(Ⅴ) and As(Ⅲ) can be restored to 97.80% and 69.61% respectively.