Preparation Of Geopolymer-Based Inorganic Membranes For Waste Water Treatment

Geopolymer is a type of amorphous state three-dimensional network gel material, which use natural mineral (kaolin) or solid waste (coal ash, slag etc.) and the synthetic silicon aluminum compounds as raw materials and consists of tetrahedral [AlO4] and [SiO4] units’ polymerization by polycondensation reaction under the condition of alkali excitation. Geopolymer is of high early strength, acid-base corrosion resistance, setting time control, excellent thermostability and work-ability. The fixed capacity of poisonous and harmful heavy metal ions by the unique three-dimensional network structure is strong and the dissolution rate is low, which has remarkable effect in the separation process of heavy metal waste water and sewage.The metakaolin-based geopolymer inorganic membrane prepared in this work has remarkable economic advantage compared with traditional commercial membrane, the preparation of low cost, raw material widely, simple preparation process, almost no "three wastes". This paper detailed investigates the main factors influencing of metakaolin-based geopolymer inorganic membrane micro-structure, pore size and specific surface area. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM), TG-DSC, BET, compressive strength and water flux testing means to characterize the structure and mechanical properties of the metakaolin-based geopolymer inorganic membrane, ultimately determined the geopolymer-based inorganic membrane optimum technological parameters which applicable to separate heavy metal ions and suspended particle pollution from waste water, and used simulation of heavy metal waste water and living waste water to study the separation ability of geopolymer-based inorganic membrane.(1) According to the preparation of raw material composition and proportion of metakaolin-based geopolymer inorganic membrane, curing temperature and the ratio of n(H2O)/n(Na2O) which may influence the micro pore structure and mechanical properties of geopolymer-based inorganic membrane was all studied. The optimum process conditions of the preparation of geopolymer-based inorganic membrane applied to membrane water treatment were determined as follows:the modulus of water-glass was 1.3, the molar ratio of Na2O and Al2O3 was 0.8, the molar ratio of SiO2 and Al2O3 was 2.96, the molar ratio of H2O and Na2O was 19, the curing temperature was 60℃ and curing time was 24 h. The each performance parameters of geopolymer-based inorganic membrane as follows:The water flux of membrane was 99.04 kg-m-2·h-1 and the compressive strength was 18.67 MPa, specific surface area was 37.87 m2·g-1, the adsorption capacity was 35.52 cm3·g-1,the average pore size was 276.11nm, the average porosity was 62.64%.(2) The study results of metakaolin-based geopolymer inorganic membrane when used in the heavy metal waste water treatment shows that:the excessive alkalinity in the geopolymer-based inorganic membrane has stronger buffering capacity to acid solution, inorganic membranes were suitable for adsorption and intercept heavy metal ions under the working conditions of the solution pH greater than 4 and the removal rate increases with the pH of solution. The removal rate of Ni2+ up to 90.82% which adsorbed by geopolymer-based inorganic membrane when the solution concentration was less than 500 mg·L-1 and pH=5. Increase the thickness of inorganic membrane and reduce the adsorption temperature and solution concentration are all beneficial to the improvement of the Ni2+ removal rate. In binary and ternary system, the adsorption rate of Ni2+ were strongly inhibited by Pb2+ and Cu2+, competitive adsorption capacity of Pb2+was the highest, the second was Cu2+, and Ni2+ was the lowest. This paper presents the primary study on the adsorption and purification mechanism of treating heavy metal waste water by geopolymer-based inorganic membrane, which are the neutralization micro-precipitation and flocculation intercept, ion exchange action and the physical adsorption effect of porous structure.(3) The research results of high turbidity waste water treated by metakaolin-based geopolymer inorganic membrane show that:comprehensive evaluation indicator system of water quality was determined by turbidity, SS and fecal coliform, and the removal rate were all more than 93%, the high turbidity water after filtration turbidity can reduced to 0.19 NTU. However, the removal rate were all lower than 70% when compared the three water quality indicators such as ammonia nitrogen, CODcr and BOD5. In addition, geopolymer-based inorganic membrane water flux decline about 22% of the initial water flux. The result shows that the geopolymer-based inorganic membrane can be effective separation of bacteria, suspended particulate matter and macromolecular organic compounds, but has poor separation effect for hydrophilic organic matter, nitrite, sulfate, ferrous salt and other inorganic small molecules reducing agents, in order to improve water quality the later work need to auxiliary introduce traditional biological-chemical method.