چكيده به لاتين
There are different ways to remove heavy metal ions from water; among these ways, memranes have attracted many attention and showed better results, but nanofiltration and reverse osmosis membranes which are used for this purpose need high applied pressures and though cause high cost. Though, researchers are concentrated on modifying the membrane technology. Adsorptive membranes have attracted many attentions because of gathering the advantages of adsorption and membrane technology. They show high efficiency, high permeability, low energy consumption and so low cost. Many researches have been done on polymeric adsorptive membranes but not on ceramic ones. In this research, the goal was to study the effect of additives on the properties of clay membranes inorder to synthesize adsorptive microfiltration clay membranes. Though, bentonite was used due to the adsorptive aluminosilicate phases formed in bentonite bodies after firing. At first, different mixtures of raw and calcined bentonite were pressed and fired at different temperatures and their properties were studied. It was seen that in each temperature, the increase in the amount of calcined bentonite caused the shrinkage and bulk density to decrease, the porosity and water adsorption to increase and the flexural strength to decrease. It means that for example after firing the samples at 1100˚C, by increasing the amount of calcined bentonite from 0 to 100%, the percentage of open porosities increased from 18.5% to 33.5% and the flexural strength decreased from 33.44 MPa to 9.05 MPa. So, the mixture of 33% of calcined bentonite and 66% of raw bentonite, fired at 1100˚C, with 26.4% of open porosities percentage and flexural strength of 26.1 Mpa, was known as the optimum composition at the first step. Calcium and magnesium carbonates were also used to simultaneousely increase the porosity and the mechanical strength besides forming adsorptive calcium and magnesium silicate phases (pyroxenes). After pressing the samples with hydraulic press and firing them at 1100˚C, their physical and mechanical properties were verified and it was seen that they were in the proper range of microfilteration membranes (i. e. the mean size of the porosities, the apparent porosities percentage and the flexural strength were in the range of 0.6-1.4 µm, 32-35% and 29-37 MPa, respectively). It was also seen that the desireble phases (i. e. anorthite, wollastonite and enstathite) were formed in the samples and were well distributed. Then the efect of the composition of the samples and also the rate of water passage on the adsorption of Cr3+ ions were verified in two different ranges (i. e. drinking water range and tannery effluent range) and it was seen that while the free carbonate sample (i. e. sample R2C) could reduce the Cr3+ ions concentration from 1000 ppm to 860 ppm, the optimum sample reduced them from 1000 ppm to 0.3 ppm. It was also seen that by decreasing the water passage rate, the water was better treated. Inorder to increase the adsorption tendency of these membranes, a bentonite-CMC layer was coated on them and the coating was stabilized with glutaraldehyde and dried at 60˚C. Then the ability of the coated and non-coated samples in Cr3+ removal from water in three different water flows and two ranges of Cr3+ ions (Drinking water range (5 ppm) and tannery effluent range (1000 ppm)) and also in treatment of high polluted water (including Cr3+, Zn2+ and Ni2+ ions, 1000 ppm of each ion) was studied and it was seen that the potimum sample (named R2C-Ca20-10%) treated the high polluted water near to gain deionized water.
