Powder activated carbon was modified with three different cationic surfactants; Cetylpridinium chloride (CPC), Hexadecyltrimethyl-ammonium bromide (CTAB) and Hexadecyltrimethyl-ammonium chloride (CTAC) for bromate removal from water. Modification of powdered activated carbon with cationic surfactants enhanced the positive charge on the activated carbon surface. Zeta potential values for surfactant modified powder activated carbon(SM-PAC) with CPC, CTAC and CTAB were 52.45mv, 50.85mv and 44.45mv respectively. However that increased in zeta potential slightly decreased the B.E.T surface area of surfactant modified powdered activated carbon(SM-PAC).Cationic surfactant adsorption on powder activated carbon (PAC) was dependant on activated carbon surface functional group, surfactant organic chain length and presence of counter ion on the surfactant .Surfactant having large number of CH2 - group like CPC showed high adsorption on PAC surface(1.32mmol/g) than that of CTAC(0.82mmol/g) and CTAB(0.95mmol/g) with smaller chain length. Surfactant with Br- as counter ion like CTAB showed high adsorption than its counterpart with Cl- as counter ion like CTAC. Among the surfactant, 1.132 mmole/gm of CPC was adsorbed while CTAC and CTAB had 0.80 and 0.92mmole/gm of adsorption on PAC respectively. Temperature effect the modification process of PAC with surfactant. In case of CPC, amount of surfactant adsorbed decrease with increase in temperature while for CTAC and CTAB, adsorption increase with increase in temperature. Maximum bromate removal was attained in case of CTAC modified SM-PAC due to high zeta potential value of SM-PAC and Cl- as counter-ion. Main mechanism for bromate removal is electrostatic interaction and ion-exchange. So counter -ion on the surfactant played an important role. In case of Cl- as counter ion, bromate removal is higher than that of Br- as counter ion on surfactant. SM-PAC modified with CTAC had 35.742mg/g of bromate adsorption capacity while SM-PAC modified with CPC and CTAB showed 34.171 and 13.11mg/g respectively. Surfactant having Cl- as counter ion showed high kinetics rate constant as compare to surfactant with Br- as counter-ion.SM-PAC modified with cationic surfactant having Cl- as its counter ion offered an advantage of Br- elimination after fixing the bromate problem. Kinetics rate constant of SM-PAC are higher than PAC due to different bromate removal mechanism. pH of solution affected the removal of bromate in case of both SM-PAC and PAC. Removal efficiency is high in the low pH. With increase in pH of solution, removal efficiency decreased. With increase in temperature of system, removal efficiency increased. However at high temperature surfactants desorption was observed. Cationic surfactant modified powder activated carbon(SM-PAC) showed high removal efficiency almost twice than those of conventional adsorbent like PAC and GAC.
본 연구에서는 계면활성제로 개질된 분말활성탄(SM-PAC)을 이용하여 브롬산 염을 제거하였다. 양이온 계면활성제로는 CPC, CTAC, CTAB가 이용되었으며, 각각의 계면활성제로 개질된 SM-PAC의 제타전위는 52.42, 50.85 그리고 44.45mV로 전기적 양성을 나타내었다. 또한 양이온 계면활성제의 흡착 이후에 분말활성탄의 표면적이 감소하나, 활성탄의 제타전위에는 크게 영향을 미치지 않았다. 활성탄에 흡착되는 계면활성제의 양은 유기탄소의 길이와, counter ion 종류에 따라서 달라진다. 유기탄소 길이가 긴 CPC는 높은 흡착량을 나타내나, 유기탄소가 적은 CTAC와 CTAB는 비교적 낮은 흡착량을 보였다. SM-PAC 중 CTAC가 가장 브롬산염의 흡착에 효과적이다. 이는 CTAC로 개질된 활성탄의 양성이 강하며, counterion이 Cl-이기 때문이다. CTAC, CPC 그리고 CTAB로 개질된 활성탄의 브롬산염 흡착량은 34.74, 34.171 그리고 13.11 mg/g과 같다. SM-PAC는 모두 일반 활성탄에 비해서 빠르게 브롬산염을 제거할 수 있고, 일반 활성탄이 브롬산염(BrO3-)을 제거할 때 발생하는 브롬(Br-)에 의한 2차 오염 문제를 해결할 수 있다. SM-PAC를 이용 시, pH의 증가는 브롬산염 제거 효율을 감소시켰으며, 온도 증가에 따라서 제거율은 증가하나 계면활성제의 탈착이 관찰되었다. SM-PAC는 기존의 브롬산염 흡착제인 활성탄에 비해 2배 이상 좋은 제거율을 보였다.