Research On Modified Diatomite Removal Of Cr (Ⅵ) In Raw Water

With the rapid development of society and the people’s living standard, the requirement of drinking water is higher and higher. In our country or even the world, the phenomenon of poisoned by the Cr (VI) ranges a large area. The conventional treatment is by making the Cr (VI) reduction to trivalent chromium, the Cr(OH)3will be remove as the precipitate. As this traditional method is difficult to meet the demands of reality, it is so important to study a new way to solve it. Natural diatomite is rich in China, and with a low price. It is often used as adsorbent for water treatment because of its huge surface area. As the adsorption property of diatomite is limited, the researchers all over the world have paid their attention to the method to improve the adsorption proper by by modified.This paper studied on Cr (VI) removal from raw water with the adsorbent of modified diatomite, including static and dynamic experiments, the specific contents include the following parts:change the optimal modification conditions and methods of optimum modification method of diatomite, and selected a diatomite for the Cr (VI)’s removal as the best modified diatomite (poly hydroxy aluminum modified diatomite); poly hydroxy aluminum modified diatomite for simulation in water with Cr (VI) removal performance, and to explore the mechanism of removal; the poly hydroxy aluminum modified diatomite except Cr (VI) factor (including temperature, pH, reaction time, initial concentration of Cr (VI)); poly hydroxy aluminum modified diatomite packed column for simulation of Cr (VI) exceed the standard water dynamic experiments except Cr (VI) effect and influencing factors of (the filtration rate, filter thickness, initial concentration of Cr(VI)), and analysis its effectiveness and feasibility.The modified experimental results showed that, poly hydroxy aluminum modified diatomite to Cr (VI) removal effect is the best, CTAB modified diatomite is a little worse, but far higher than the non modified diatomite to Cr (VI) removal rate. The best modified conditin of poly hydroxy aluminum modified diatomite is:the concentration ofpoly hydroxy aluminum modified solution for0.2mol/L2h, modification time, the modification temperature is60℃, the best modified [Al]/soil molar mass is1g modified diatomite need to add50mL concentration ofpoly hydroxy aluminum solution ratio of0.2mol/L for10mmol/g. The static experimental’s results indicate that, Cr (Ⅵ) solution at the concentration of1mg/L, pH7, poly hydroxy aluminum modified diatomite dosage is0.5g, the reaction time is60min, poly hydroxy aluminum modified diatomite to Cr (Ⅵ) removal rate reached96.36%at25℃, the treated water to Cr (Ⅵ) concentrations reached the "drinking water health standards"(GB5749-2006) the requirements of0.05mg/L. Poly hydroxy aluminum modified diatomite to Cr (Ⅵ) through simulation experiment adsorption isotherm, the results found that poly hydroxy aluminum modified diatomite to Cr (Ⅵ) adsorption accords with Langmuir isotherm and the Freundlich isotherm. The poly hydroxy aluminum modified diatomite to Cr (Ⅵ) adsorption both monolayer adsorption and adsorption. The Langmuir isotherm correlation coefficient R2is0.9526, the theoretical adsorption capacity can reach196.08μg/g; Freundlich isotherm correlation coefficient R2is0.9511. Poly hydroxy aluminum modified diatomite to Cr (Ⅵ) the kinetics for the adsorption process can meet the quasi two level dynamic equation was good, the correlation coefficient R2=0.9965fitting, fitting the equilibrium adsorption capacity of qe=192.3μg/g, and measured the static experiment of poly hydroxy aluminum modified diatomite on in water with Cr (Ⅵ) adsorption capacity the maximum removal rate of192.8μg/g similar to meet, so it can be used in quasi two level dynamic equation to describe the poly hydroxy aluminum modified diatomite to Cr (Ⅵ) process of adsorption.The dynamic experimental’s results show that, polyhydroxy aluminum modified diatomite filter layer thickness is100cm, the filter column of5cm inner diameter, Cr in simulated water samples (Ⅵ) concentration is lmg/L, the filter column filtration velocity control of5mL/min poly hydroxy aluminum modified diatomite filtration column removal from simulated Cr (Ⅵ) exceed the standard samples of Cr (Ⅵ) better. In the actual production process, according to the model test and the principle of dimensional analysis, the thickness of the filter layer is suitable and good control of the filtration rate, by polyhydroxy aluminum modified diatomite for removal of Cr(Ⅵ) is effective.The regeneration experimental’s results show that NaOH regeneration of modified diatomite after three previous adsorption of Cr (Ⅵ) effect is better, can use the water concentration of Cr (Ⅵ) to "drinking water health standards"(GB5749-2006) of0.05mg/L. Diatomite after3times of Cr (Ⅵ) adsorption effect began to reduce. The reason for this is that after3times of repeated use of adsorption on the diatomaceous earth column more Cr (Ⅵ) ions. the adsorption of Cr (Ⅵ) began to decrease. Therefore, you can come to regenerate after treatment of polyhydroxy aluminium modified diatomite Cr (Ⅵ) in water has good adsorption performance.