Removal of Chromium (VI) from Aqueous Solution by Activated Carbon Modified with Cationic Surfactant Benzalkonium Chloride

Background and Chromium hexavalent compounds are carcinogens that are found in groundwater as chromate and dichromate negative ions. The aim of this study was to remove Cr (VI) from water by activated carbon modified with cationic surfactant alkyl dimethyl benzyl ammonium chloride (Benzalkonium chloride).
In terms of the Critical Micelle Concentration (CMC) of surfactant, three concentrations of Benzalkonium Chloride (BZK) including half, one and two fold of CMC were used to modify activated carbon. Modification was performed by contacting activated carbon and surfactant for 24h on the shaker. Ordinary and modified activated carbons were used as sorbents for Cr(VI) removal from aqeoues solutions. Modified Activated Carbon (MAC) by cationic surfactant and Unmodified Activated Carbon (UAC) were examined as adsorbents for Cr (VI) from aqueous solutions. Experiments were conducted in batch and continuous mode in acid (pH=4), natural (pH=7) and alkaline conditions (pH=10). Cr (VI) was measured by spectrophotometer.
Time to reach Cr (VI) adsorption equilibrium for UAC and MAC were 180 and 120 min, respectively. Cr (VI) adsorption capacity for UAC was 1.79 mg/g but in MAC the value increased to 8.87 mg/g. 5g/L of MAC modified with 2cmc of surfactant showed greatest Cr (VI) adsorption capacity in natural pH condition. Breakthrough point in the column packed with MAC enhanced 3 times compared with UAC. Adsorption isotherm was best fitted with Langmuir model and adsorption kinetics was determined as pseudo second order.
Modification of activated carbon by cationic surfactant causes increase in adsorption capacity of Cr (VI) from aqueous solution. Therefore, it could be used in removal of toxic Cr (VI) compounds from water.