| Wastewater purification has been one of the most important issues in the human society at present. Using solid absorbents to remove the metal ions is an important part and effective mean in the field of wastewater treatment, but the regeneration of the adsorbents are also a hard problem. The solid adsorbents which have absorbed the heavy metal ions could be recycled a limited number of times by different means,however, the adsorption capacity could decline. The absorbents absorbed metal ions would become a solid waste and cause a secondary pollution. Because the heavy metals are expensive, we need resolve in practice not only the problem of wastewater pollution but also the recycling and utilization of heavy metal ions.In this work, porous silica coatings on silica sand have been prepared using sodium silicate as the silicon source with varying conditions. The modified sands were characterized by SEM, XRD, N2-sorption and TG-DTA. The adsorption of nickel, cobalt and copper ion of the modified sands were studied. The modified sands adsorbed with nickel, cobalt and copper ions were used for the preparation of color glasses, and the spectra of the glasses were measured.The influence of the ingredient addition order, the reaction temperature and time as well as the quantities of hydrochloric acid, P123 and silica sands used in the synthesis system(P123-silica sand-water glass-hydrochloric acid) on the formation of silica coating was carefully investigated and the conditions were optimized. The results indicate that add hydrochloric acid solution to sodium silicate favor the formation of silica coating with large surface area. The optimized conditions for the preparation of silica coating on the modified silica sand were as 60℃ temperature, 0.4ml hydrochloric acid, 0.3g P123 and 2g silica sand. Under the best coating conditions, porous silica coating with a thickness 1.5~2μm was formed and the specific surface area of the modified silica sand could reach the maximum of 28m2/g. SEM measurements showed the edges of the modified sands turned round and the sands surface became rough. The surface coating layer mainly consisted of bending rod-like particles. In addition, the formation mechanism of the coating was studied. The results showed that the surfactant and the hydrolyzed and condensed product of the sodium silicate in acidic conditions self-assembled, followed be the deposition on the surface of silica sands.Multiple coatings were further synthesized on silica sand. Nitrogen adsorption analysis showed that the adsorption curve of modified silica sands was between Type II and VI isotherms. Studies suggested that pores in the coating layers were mainly attributed to the decomposition of surfactant and the evaporation of organic solvent in the gel. In addition, the specific surface area, weight loss, coating layer thickness and the equivalent diameter of the modified sand increased with the times of coating cycles. The specific surface area of the five-time coated sands was 131m2/g, which was 655 times than of the original silica(0.2m2/g). The thickness of the coating layer in this case was 30μm.The five-time coated silica sands were applied to absorb nickel, cobalt, copper ions from water. Factors affecting the adsorption capacity of the five-coated silica sands, such as pH value, temperature, absorption time, initial concentration of ions as well as dosage of the modified sand were investigated. The results showed that the best pH value for nickel, cobalt, copper ions respectively was 6, 6, 5. Compared with cobalt and copper ions, the temperature had an obvious effect on the adsorption efficiency of nickel ions. The absorption time almost had no effect on the adsorption capacity of the silica sand.The modified sands adsorbed 17.82 mg of nickel ions, 20.04 mg of cobalt ions and 17.28 mg of copper ions were used for glass preparation. The study found that the modified silica sand enriched enough cobalt and nickel ions to obtain color glasses. However, the copper ions absorbed were not enough to get a color glass. Further improvement of the adsorption capacity of copper ions on the modified silica sand had to be made.The results from the work provide a new idea for a comprehensive solution waste water purification, secondary pollution of the used absorbents and reutilization of the metal ions in waste water. Using the silica sands absorbed metal ions from water to introduce colorants for color glass preparation, on the one hand, reduce the production cost, and on the other hand, could permanently immobilized the poisonous metal ions, leading to a good solution to solve the metal ions contamination in water. |
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