|其它题名: ||Phosphate removal by blast furnace slags adsorption|
|作者: ||王子婕;Wang, Tzu-Chieh|
|关键词: ||磷;轉爐石;脫硫渣;等溫吸附;動力吸附;Phosphate;BOF slag;desulphurization slag;Freundlich isotherm;absorption kinetic|
|上传时间: ||2015-05-04 10:03:09 (UTC+8)|
|摘要: ||轉爐石(BOF)與脫硫渣(DS)為鋼鐵製程之爐渣副產物且為廉價的吸附劑，本研究以磷酸鹽配製含磷人工水樣，轉爐石與脫硫渣取自中國鋼鐵公司，採等溫吸附實驗探討轉爐石與脫硫渣去除水中磷，吸附操作參數包含水洗、pH、BOF與DS添加量、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，以能量散佈分析儀(EDS)與熱游離式掃描式電子顯微鏡(SEM)分別測定BOF與DS之化學成份組成及表面特性。|
EDS研究結果顯示BOF與DS化學成份組成Ca之重量百分比分別為12.6%與25.9%，於水中會溶出鈣且pH大於11，與磷形成Ca5(PO4)3(OH) (s)沉澱物，且因DS鈣溶出量為BOF鈣溶出量之約3倍，DS去除磷能力約為BOF之1.6倍。BOF與DS水洗前與水洗後之磷去除率分別為95-99%與20-60%，顯示水洗前BOF與DS以Ca5(PO4)3(OH) (s)沉澱型態去除為主。經水洗轉爐石(BOFW)、經水洗脫硫渣(DSW)亦具有吸附去除磷的功能，BOFW與SDW表面仍含Ca之重量百分比分別19.0%與20.8%，Freundlich等溫吸附結果顯示DSW之磷吸附量約為BOFW之3-4倍，pH對BOFW與SDW吸附磷最佳pH 為10，此乃因於表面形成Ca5(PO4)3(OH)(s)沉澱物，DSW 及SEM亦顯示BOFW與DSW表面有Ca5(PO4)3(OH) (s)沉澱物。BOFW與DSW對磷吸附動力學遵循Lagergren擬二階動力吸附模式，DSW之二階動力常數k2值小於BOFW之k2值。BOFW之內部孔隙擴散k1值大於DSW之k1值，磷於DSW之內部孔隙擴散速率大於BOFW。綜合上述BOF與SD可有效去除水中磷，且DS去除磷能力優於BOF。
Slag is a by-product from steel factory and is a low-cost adsorbent. This study evaluates the adsorption removal of phosphate from aqueous solution by slags. Basic oxygen furnace steel slag (BOF) and desulfurization slag (DS) from The China steel company and phosphate-containing synthetic water are used in this study. The operational parameters include water washed, pH, type and dosage of slag (BOF and DS), initial concentration of phosphate, and contact time. All experiments are conducted by the isotherm adsorption test. The adsorption kinetic of phosphate by slags are evaluated by the Freundlich isotherm, the Lagergern pseudo-second-order and Intraparticle diffusion models. Furthermore, the chemical composition and surface morphology of slags are examined by energy dispersive spectrum (EDS) and scanning electron microscopy (SEM), respectively.
The results of chemical composition from EDS test show that BOF and DS contained 12.6% and 25.9% of Ca (wt%), respectively, which released Ca ions from the slags into solution to induce high pH levels to above 11. The released Ca ions could react with P to form the precipitation of Ca-phosphate compounds. The P removal capacity (PRC) of DS was about 1.6 times of that of BOF because the amount of released Ca ions of DS was about 3 times of that for BOF. Non-washed BOF and DS slags could remove 95-99% of P, as compared to washed BOF and DS slags (BOFW and DSW), which could remove 20-60% of P. It indicates that phosphate removal of non-washed BOF and DS slags occurred predominantly via the precipitation of Ca-phosphate compounds. The SEM micrographs show that Ca-phosphate compounds precipitated on the slag surface. The adsorption of P by BOFW and DSW followed the Freundlich adsorption isotherm model. The optimum pH for adsorption of P was at 10 and the removal ratio could reach more than 80%. The amount of adsorbed P of DSW was 3-4 times higher than that of BOFW. Moreover, the adsorption kinetic of P by BOFW and DSW well followed pseudo-second-order and intraparticle diffusion models. The pseudo-second-order adsorption rate constant, k2 value of DSW was larger than that of BOFW. In contrast, intraparticle diffusion rate constant, ki value of DSW was smaller than that of BOFW. It implies that intraparticle diffusion rate of P by DSW was higher that of BOFW. Overall, both BOF and DS could remove P effectively and the PRC of DS was better than that of BOF.