## 【英文概要】

· 研究課題名 = 「Selective recovery of rare metals from plating waste solution using sulfur-impregnated adsorbent prepared from waste biomass」

· 研究代表者名及び所属＝Takaaki WAJIMA (Chiba University)

## ·要旨

A novel carbonaceous adsorbent for removal of heavy metals was prepared from industrial wastes (paper sludge and heavy oil ash) and waste biomass (rice husk, rice straw and cedar bark) using sulfur impregnation for the recovery of rare metal (nickel) from nickel plating waste solution. In the case of paper sludge, sludge was treated with 5 M HCl to remove inorganic content, and then immersed in 1 M K₂S solution to prepare sulfur-impregnated sludge. The immersed-sludge was heated at 100 - 1000 °C for 1 hour in nitrogen gas to the sulfur-impregnated adsorbent by pyrolysis. The properties and abilities of sulfur-impregnated adsorbent to remove the heavy metals were examined. The sulfur-immersed sludge with high sulfur content can be prepared by immersing in K₂S solution. The product pyrolyzed at 400 °C has a maximum removal ability for nickel and lead ion, which has high specific surface areas with sulfur-based functional. The product pyrolyzed at 400 °C indicates more effective removal for heavy metals of all cations, Zn²⁺, Cu²⁺, Ni²⁺, Pb²⁺, Mn²⁺, Co²⁺, Sr²⁺, Fe³⁺, Al³⁺ and Cr³⁺, than commercial charcoal, while not effective for heavy metals of almost oxi-anions. The product shows the high removal ability for lead and nickel ions from aqueous solution, and high selective removal ability depending on pH of the solution. In the case of heavy oil ash, raw ash was immersed in 1 M K₂S solution or 1 M KOH solution for 24 h, and then heated at 100 - 1000 °C for 1 h under N₂ atmosphere. After cooling to room temperature under N₂ atmosphere, the obtained solid was washed with distilled water, and dried in a drying oven to obtain the product. Regardless of pyrolysis temperatures, the sulfur content of the product using K₂S (Product-K₂S) is higher than that of the product using KOH (Product-KOH), and lead removal ability of Product-K₂S is higher than that of Product-KOH, while specific surface area of Product-K₂S is lower than that of Product-KOH. The product-K₂S obtained at 300 °C (Product-K₂S-300) shows the highest adsorption of lead from aqueous solution, and high selective removal for lead ions in ternary Pb²⁺-Cu²⁺-Zn²⁺ solution. The equilibrium capacity of the product-K₂S-300 was extrapolated using Langmuir and Freundlich isotherm models, and the experimental data are found to fit Langmuir than Freundlich. In ternary Pb²⁺-Cu²⁺-Zn²⁺ solution, the order of adsorption using the product-K₂S-300 is Pb²⁺ > Cu²⁺ > Zn²⁺, and with increasing the pH of the solution the removal of Pb²⁺ and Cu²⁺ increase. In the case of biomass wastes, these wastes were cut, and then immersed in K₂S solution to prepare sulfur-immersed materials. The immersed-materials were heated at 100-700 °C in nitrogen gas to produce the sulfur-impregnated adsorbent by pyrolysis. The properties and abilities of sulfur-impregnated adsorbent to remove the heavy metals were examined. The sulfur-immersed materials with high sulfur content can be prepared by immersing in K₂S solution. In pyrolysis, with increasing the heating temperature to 400 °C, sulfur content of the product decrease, and then above 400 °C those are almost constant, while carbon content of the product decrease between 400-600°C. The product prepared at 300-400 °C has a maximum removal ability for nickel ion, and can recover nickel ion from plating waste solution.

・キーワード＝ Waste Biomass, Sulfur-impregnated adsorbent, Metal recovery, Plating waste solution, Selectivity