Study On Preparation Of Modified Attapulgite And Treatment Of Humic Acid In Micro-polluted Water

In recent years, the technology of water analysis was advanced gradually, so more and more micro-polluted substances in the water sources would be discovered. In this situation, in order to protect people’s health from polluted water, micro-polluted water treatment has become a current hot research.Large amount of natural organic mater existed in the water, such as humic substances which was an important reducing organic matter. Humic acid would has a series of physical and chemical reactions with other substance. It not only affected water colour, but also reduced the removal ability of coagulant to colloidal particles suspended during the conventional water treatment process. More seriously, humic acid would turn into various halides, and most of them were carcinogens or mutagens.This paper based on the traditional water treatment process, as well as no new structures and no pre-chlorination disinfection. Selecting attapulgite which has the properties of rich, low cost, good settling, adsorption, bleaching, filling, rheology and ion exchange. The attapulgite were modified by acid activation, heat treatment and octadecyl trimethyl ammonium chloride (OTAC) organic modificaiton. After orthogonal experiment, the optimum conditions of modification were listed as follows:3 mol/L acid reacted 3h,0.5 mol/L of the sodium chloride concentration,2 hours of the sodium treatment,3 percent of the natural attapulgite’s quantity as the quantity of modifier,9 minutes of the microwave modified time, microwave frequency was 100Hz. The removal efficiency of humic acid could reach 97 percent when the dosage of modified attapulgite was 0.7 g/L.The raw and modified attapulgite were characterized by infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that acid activation influenced the selective adsorption of attapulgite, moreover, attapulgite structure was transformed from a block structure to a lamellar structure with some fragmentation. Some of the water in the samples was lost after heat treatment, it also created a loose and expended lamellar structure. After organic modification, attapulgite took advantage of electrostatic forces to adsorb positively charged organic modifier, and its structure and morphology would not be changed significantly. "Acid+heat+organic" combined modification damaged internal structure of attapulgite, result in modified attapulgite loading the least amount of OTAC.This paper studied the humic acid adsorption properties of modified attapulgite. And researching the adsorption efficiency which were affected by different modified attapulgite dosage and pH value. Used Langmuir, Freundlich, Temkin, Redlich-Peterson isotherm to fit the adsorption isotherms of modified attapulgite, and the research results could be gain as follows:(1) Through considering the attapulgite adsorption capacity, removal efficiency and economic factors, the best modified attapulgite dosage was 0.4g/L when adding attapulgite alone. (2) Modified attapulgite has the better removal rate in the acid water, while it has the worse removal rate under the neutral water. It should be combined with PAC when it were used in enhanced coagulation sedimentation process. (3) Modified attapulgite have best settling property in 90 min, it was great to improve the removal rate of natural organic in the coagulation sedimentation process. (4) Used four kinds of siotherm equations to fit the adsorption isotherm of modified attapulgite. The comparison of fitting coefficient was:Langmuir> Redlich-Peterson> Temkin> Freundlich. Langmuir isotherm equation has the largest correlation coefficient, so it could illustrate the process of humic acid adsorption better. Modified attapulgite preferred to monolayer adsorption. Moreover, it was the beneficial non reversible adsorption.After PAC combined with modified attapulgite in the water treatment, the removal rate of humic acid and turbidity in the micro-polluted water has been researched. Meanwhile, finding the best dosage of modified attapulgite coagulant to remove the humic acid and turbidity. Observing the removal efficiency of humic acid and turbidity in different settling time, initial turbidity, pH value, adding order and hydraulic conditions. The results have been found as follows:(1) "PAC-modified attapulgite" enhanced coagulation process can reduced PAC dosage, reduced settling time, expanded scope of pH and effectively improve the removal rate of humic acid and turbidity, and it had high economic and practicality. (2) Compared with adding PAC alone, "PAC-modified attapulgite" could reduce 25% PAC. When the dosage of PAC was 15mg/L, modified attapulgite was 30mg/L and the optimal settling time was set as 30 minutes,95.5% of humic acid and 96.8% of turbidity of raw water could be removed. (4) Appropriate initial turbidity could effectively improve removal rate of humic acid, while the low initial turbidity was not conducive to the removal of humic acid and turbidity. (5) Enhance coagulation preferred "ex-adding" process:it meant adding modified attapulgite first, then mixing rapidly, and adding PAC last.