| Preparation of granulated composite materials using clay minerals and industrial wastes for treatment of electroplating industrial wastewater was studied in this paper.lt was the development of environment-friendly mineral adsorption materials. The issue aimed at solving heavy metal pollution caused by electroplating industrial waste water, and at the same time, it opened an effective way for the comprehensive utilization of clay minerals and fly ash of industrial wastes. The research topic was of important theoretical significance and practical application value.The preparation conditions for montmorillonite/fly ash granulated adsorption materials and the treatment of electroplating industrial wastewater containing Cu2+, Zn2+, Ni2+ and Cr6+ heavy metal ions were studied systematically in this paper. The materials were characterized by using XRD, SEM, DTA/TG, BET etc. The adsorption/desorption rules were studied with the particulate composite adsorbing materials to treat electroplating industrial wastewater containing a variety of heavy metal ions. The adsorption dynamic equation, thermodynamic parameters, and mechanism were discussed for the removal of heavy metal ions by using granulated adsorption materials.The main research achievements were as follows:1 Study on preparation of granulated adsorption materials(1) The optimum preparation process conditions for preparation of granulated adsorption materials of montmorillonite/fly ash were a ratio of montmorillonite to fly ash of 6:4, a calcination temperature of 450℃, a calcination time of 0.5h, additive industrial starch of 10% and the particle diameter of 1～2mm. When the granulated adsorption materials prepared under the above mentioned conditions were used to treat waste water of 200mg/L initial concentration containing Cu2+, its adsorption ratio was up to 96.34% and the loss ratio was less than 1%.(2) The optimum preparation process conditions for the preparation of granulated adsorption materials of attapulgite/fly ash were a ratio of attapulgite to fly ash of 6:4, a calcination temperature of 400℃, the additive ratio of sodium silicate and starch of 15% and 10% respectively. When the granulated adsorption materials prepared under the above mentioned conditions were used to treat waste water of 50mg/L initial concentration containing Zn2+, the adsorption ratio was up to 94.23%, and the loss ratio was 4.33%.2 Characterization of granulated adsorption materials(1) XRD pattern of the montmorillonite/fly ash granulated adsorption materials prepared under the optimum process conditions showed that the mineral phases were not changed before and later calcination. Montmorillonite mainly lost its adsorption water and interlayer water, which was observed from the DAG/TG pattern. SEM images analysis showed that there was hardly porous structure in granulated materials before calcination, but there were obviously porous structure and pore sizes of 20 to 50μm in granulated materials after calcination. The physical tests and analysis of granulated adsorption materials showed that the density was 1.47 kg/m3, water absorption capacity was 31.80%, apparent porosity was 46.82%, compressive strength was 5.28 MPa, and the surface area was 10.28m2/g.(2) XRD pattern of the attapulgite/fly ash particles adsorbed materials obtained under the appropriate conditions showed that the mineral phases were not changed before and after calcination. Attapulgite mainly lost its adsorption water and interlayer water, which was observed from the DAG/TG pattern. SEM images analysis showed that the granulated material had good porous structure, and pore sizes were from 10 to 30μm. The physical tests and analysis of granulated adsorption materials showed that the density of the granulated adsorption materials was 1.11 kg/m3, water absorption capacity was 32.89%, apparent porosity was 54.77%, compressive strength was 2.15 MPa, and the surface area was 17.01m2/g.3 Treatment of wastewater containing a single heavy metal ion with granulated adsorption materialsThe optimum conditions for granulated adsorption materials of montmorillonite/fly ash to remove heavy metal ions under orthogonal experiment were the amount of adsorbent dosage was 12g·L-1,20g·L-1,24g·L-1 and 20g·L-1 respectively; pH was 6,7,7 and 3 respectively; reaction time was 80min.When the initial concentration of Cu2+, Zn2+,Ni2+,Cr6+ was 100 mg·L-1,25 mg·L-1,20 mg·L-1 and 10 mg·L-1 respectively,the adsorbent ratio of removal of Cu2+,Zn2+,Ni2+,Cr6+ was 99.00%,99.10%,98.90% and 99.36% respectively under the optimal experimental conditions.4 Treatment of electroplating industrial wastewater with granulated adsorption materials(1) The optimum conditions for granulated adsorption materials of montmorillonite/fly ash to remove heavy metal in electroplating industial wastewater were the amount of granulated adsorption materials dosage was 0.05/cm3, pH was 6.5, and reaction time was 80min. The adsorbent removal rate of Cu2+,Zn2+,Ni2+,Cr6+ was 98.19%,98.07%,98.81%,and 99.06% respectively under the optimal experimental conditions. These residual concentrations of heavy metals waste water treated were lower than the first standard of the national waste water discharge (GB8978-1996).(2) The optimum conditions of using attapulgite/fly ash particles adsorbing material to remove heavy metal in electroplating industrial wastewater were granular adsorbent dosage was 0.07 g/cm-3, pH was 6.5, and reaction time was 80min. The removal ratio of Cu2+,Zn2+,Ni2+,Cr6+ was 98.14%,87.79%,97.52% and 97.58% respectively under the optimal experimental conditions. These residual concentrations of heavy metal wastewater were lower than the first standard of national wastewater discharge (GB8978-1996).5 Study on regeneration and reuse of granulated adsorption materialsThe effect of desorption and regeneration of two kinds of granulated adsorption materials was the best when using 1mol·L-1NaCl among several different desorption agents. The adsorptive ratio of granulated adsorption materials to remove heavy metal ions decreased slightly and the loss ratio was about 10% after six regeneration and reuse, which showed that the effects of two kinds of granulated adsorption materials were better after desorption and regeneration.6 Discussion of mechanism of adsorption of heavy metal ions on granulated adsorption materials(1) The reaction of adsorption with granulated adsorption materials of montmorillonite/fly generally was a first order reaction kinetics equation C1= C0·e-kt, which showed that the adsorption was mainly controlled by liquid membrane diffusion. As the adsorption thermodynamic parametersΔH<0,ΔS <0 andΔG<0 showed that rising temperature was not conducive to a positive reaction, which showed that the decrease ofΔG was the main driving force for the removal of the heavy metal ions.The adsorption data of granulated adsorption materials of montmorillonite/ fly fit with Freundlich and Langmuir adsorption isotherm models, and the correlation of Langmuir adsorption isotherm model was better.(2) The mechanism that heavy metal ions were adsorbed by montmorillonite was mainly ion-exchange adsorption. There were mainly three kinds of forms that the heavy metal ions were adsorbed by attapulgite, which were surface oxygenation, micro-pore channel and attapulgite crystal structure. Fly ash adsorbed metal ions could be divided into three forms:physical adsorption, chemical absorption and adsorption-flocculation sedimentation synergy.(3) Study on mechanism of adsorbent velocity of granulated adsorption materials showed that the adsorption velocity of adsorbent material in fluid could be divided into three stages, which were external diffusion, pore diffusion and adsorption reaction, and the slowest stage of pore diffusion process was the main control stage.
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