|摘要: ||本研究探討爐渣去除含磷，脫硫渣(desulfurization slag, DS)與電弧爐氧化渣(electric arc furnace slag, EAF)分別取自中國鋼鐵公司與中龍鋼鐵公司，採等溫吸附實驗探討DS與EAF去除水中磷，吸附操作參數包含DS與EAF添加量、pH及接觸時間等。吸附實驗結果以Freundlich等溫吸附公式、Lagergern 擬二階(Pseudo-second-order)動力與內部孔隙擴散速率(Intraparticle diffusion model)模式評估吸附水中磷之動力。此外，測定DS與EAF之化學成份組成、表面特性及比表面積。|
研究結果顯示DS化學成份組成鈣之重量百分比與比表面積分別為25.9%與10.79 m2/g , EAF則為19.9%與 0.97 m2/g。DS於水中會溶出鈣且pH大於10，與磷形成Ca5(PO4)3(OH) (s) (hydroxyapatite, HAP) 沉澱物，且DS之鈣溶出量為EAF之約12-18倍。因DS比表面積與鈣溶出量皆甚大EAF，故DS去除磷能力約為EAF之189倍。DS與EAF去除磷最適pH為10，SEM亦顯示DS與EAF表面有HAP沉澱物。由於DS之鈣溶出量高可形成HAP沉澱物，故去除磷主要機制為沉澱；相對地，EAF之鈣溶出量低，磷初始濃度高時無足夠鈣生成HAP，故去除磷主要機制為吸附。DS及EAF對磷吸附遵循Freundlich等溫吸附，DS之Freundlich常數KF值大於EAF；動力吸附則遵循Lagergren擬二階動力吸附與內部孔隙擴散模式，DS之平衡吸附量(qe)與內部孔隙擴散速率(ki)值皆大於EAF。綜合結果顯示DS去除磷能力優於EAF。
This study evaluates the adsorption removal of phosphate from aqueous solution by slags. Desulfurization slag (DS) and electric arc furnace slag (EAF) sampled from The China steel company and Dragon Steel company, respectively, were used to treat phosphate-containing synthetic water. The operational parameters include, and dosage of DS and EAF slags, initial concentration of phosphate, pH and contact time. All experiments were conducted by the isotherm adsorption test. The adsorption kinetic of phosphate by slags were evaluated by the Freundlich isotherm, the Lagergern pseudo-second-order and Intraparticle diffusion models. Furthermore, the chemical composition, surface morphology and specific surface area were measured.
The results show that chemical composition of Ca (wt%) and specific surface area of DS were 25.9% and 10.79 m2/g, respectively, and those were 19.9% and 0.97 m2/g for EAF. DS released Ca ions and induced pH of slag solution above 10. The released Ca ions could react with phosphate to form Ca5(PO4)3(OH)(s) (hydroxyapatite, HAP) precipitates to remove phosphate. The amount of released Ca ions of DS was about 12-18 times of that for EAF. Due to the specific surface area and amount of released Ca ions of DS were great larger than those of EAF, the phosphate removal capacity of DS is about 189 times of EAF. The optimum pH for phosphate removal is about 10 and SEM examination showed that HAP precipitates onto surface of both DS and EAF. The phosphate removal of DS is dominated by precipitation because DS releases higher Ca ions to form HAP precipitates. In contrast, phosphate removal of EAF is dominated by adsorption due to the released Ca ions being not enough to form HAP precipitates for higher initial phosphate solution. The adsorption of phosphate by DS and EAF followed the Freundlich adsorption isotherm model. The adsorption capacity (KF) value of DS was larger than that of EAF. Moreover, the adsorption kinetic of phosphate by DS and EAF well followed pseudo-second-order and intraparticle diffusion models. Both of equilibrium adsorption capacity (qe) and intraparticle diffusion rate constant (ki) values of DS were larger than those of EAP. It is concluded that phosphate removal capacity of DS was better than that of EAF.