| It is an urgent demand that tanning wastewater cannot meet the emission standards due to the use of a large number of chrome tanning agent. Compared with electronic electroplating, mining, metallurgy and other "heavy mental-comtaining" industry wastewater, leather wastewater contains a lot of neutral salt, high organic components and complicated form of chromium. It is needed that the adsorbent has selective adsorption efficiently in disposal wastewater containing low concentration of chromium and neutral salt when using traditional adsorption method. At the same time of the adsorbent also should have certain universality for organic chromium complex and polymers. Previous studies have found that zirconium (Zr) intercalated modified montmorillonite (MMT) composite adsorbent has the advantages of the above two aspects. But the problem of powdery adsorbent running away with wastewater in the process of application are also exist in this study, and has an impact on the adsorption performance. Therefore, the gelcasting of Zr-MMT powder was studied in this study on the basis of optimizing Zr modified MMT. And adding in the glass powder in molding process to increase the intensity. The adsorption characteristics of before and after adsorption of Cr(Ⅲ) in the presence of EDTA, glycine and formic acid have been carried out. The main conclusion includes the following several aspects:(1)In the optimization experiment of Zr-MMT, the ratio of Zr to MMT, modification temperature, and sintering temperature can effect the adsorption of MMT by change the layer spacingt. Different proportions of Zr intercalated MMT can change the interlayer of MMT significantly, and there is a maximum. When the radio of Zr to MMT was 2:5, the maximum adsorption amount was of 8.79mg/g. Modified temperature had little effect on the adsorption and low temperature was conducive to adsorption reactions. Modification temperature and sintering temperature also have an obvious influence on MMT layer spacing. With the temperature increasing, the layer spacing have a downward trend, its decline mainly because of the changing of the hygroscopic and expansion of MMT. When the modification temperature≤70℃, the sintering temperature≤ 600, the layer spacing changes had little impact on the adsorption Cr (Ⅲ). When the sintering temperature rise to 800 ℃, ZrO2 in MMT layers morphology transform, interlayer structure damage, the adsorption quantity had fallen sharply. The best sintering temperature is 500 ℃, at this point, specific surface area of the Zr-MMT increased from 30.8 m2/g to 39.5 m2/g. In the process of the temperature modification, Zr intercalated MMT did not change the electronegative of MMT. When the pH>6, Zr hydroxide and MMT synergy make Zr-MMT electronegativity stronger, and conducive to the adsorption of cationic heavy metals. The adsorption of chromium can make layer spacing increases.(2)The ratio of Zr to MMT, polystyrene molding ball quantity, foaming agent and sintering temperature was studied in using gelcasting molding method. The effect of porous forming Zr-MMT (P-Zr-MMT) of shrinkage, porosity, Zeta potential, the surface area and the distance between layers change on the quantity of adsorption are analyzed in the experiment. The results showed that polystyrene ball quantity of porous forming P-Zr-MMT greatly influenced the degree of shrinkage, porosity, the difference was about of 20% or more. This is mainly because that the polystyrene ball volatile after high temperature sintering. The eventually forming parameters is Zr:MMT= 2:5, PS= 30 ml, frother= 1.65 g, sintering temperature= 600 ℃, Compared with the powder, the forming porous P-Zr-MMT had lower surface area, and the polystyrene ball after high temperature sintering part of carbonation, the surface Zeta potential decreased by about 22%, but the electronegativity is enough to meet the requirements of chromium adsorption, its stability in the water can meet the requirements, and high porosity, pore size, uniform distribution uniformity.(3) Through the adsorption study of Zr-MMT and P-Zr-MMT in the presence of the organic matter, EDTA as the strongest heavy metal chelating agent can form a stable chelate. With the increase of content of EDTA, the adsorption rate of Cr (Ⅲ) slash, but even when EDTA:Cr= 5:1, Zr-MMT and P-Zr-MMT adsorption of Cr(Ⅲ) has little different with other two ligands. Glycine and formic acid has no effect on adsorption of chromium even when the ratio increases to 20:1. Zr-MMT and P-Zr-MMT has more extensive adaptability. In the process of adsorption, organic ligand can enter interlayer with Cr (Ⅲ), and make MMT layer spacing increased. organic complexes made the charge of Cr3+ decline, but still can meet the needs of low concentration of chromium-containing waste water treatment. The removal rate can reach more than 80%. It is the result of the electrostatic adsorption and chemical precipitation.In above research, it is provides a new type of high selection, strong adaptability, good water stability porous adsorption material, solved the problems of powdery adsorbent hydraulic loss. It also provide the engineering basis for the advanced adsorption bed reactor. |
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