Synthesis of a biochar based adsorbent from dichrostachys cinerea pods for the removal of selected Organic pollutants from chemical refinery effluent water
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The process of chemical refining of coke oven by products (crude tar and crude benzole) generates a lot of process waste water since water is immensely used at most of the refining stages. The waste water generated is highly contaminated with organic pollutants such as benzene, toluene, xylene, indene, thiophene, naphthalene, ethyl benzene and others. These contaminants if not monitored, controlled or eliminated from the process waste water end up in both terrestrial and aquatic environments as well as the atmosphere endangering the health of both flora and fauna as these substances are known carcinogens. Several methods have been recommended for the removal of organic contaminants from process waste water including adsorption techniques using adsorbents synthesized from agricultural or forestry plant derived materials. Different adsorbents were synthesized by chemically activating bio char samples at different activating temperatures using potassium hydroxide as the chemical activating reagent. Samples of dry Dichrostachys cinerea pods were collected from trees and underneath trees from the forests around Redcliff town in the midlands town of Kwekwe for use as biomass. The Biomass was tested for its chemical profile including moisture content before charring it at different temperatures of 400 oC, 500 oC and 600 oC for optimum bio char yield. Bio char prepared at 500 oC was chemically activated with potassium hydroxide at three different activation temperatures of 400 oC, 600 oC and 700 oC. The synthesized adsorbents were characterized by FT-IR and Scanning electron microscopy (SEM) before their sorption efficacies on indene; thiophene and ethyl benzene was evaluated. Varying the chemical activating temperature resulted in different functional groups on the three synthesized adsorbents. Adsorption studies (adsorption efficacy, adsorption isotherms, batch and column) were carried and all the synthesized adsorbents showed adsorption efficacies ranging from 70 % to 85 % to adsorb all the pollutants. Qualitative and quantitative information on the above stated adsorption studies was obtained through both spectroscopic (UV-VIS) and chromatographic (GC-FID) methods of analysis. All the adsorption experiments fitted the Freundlich model better compared to the Langmuir model. It was statistically proven that there was no significant effect of changing the chemical activating temperature on the adsorption of indene and thiophene while changing of this parameter caused significant differences on the adsorption of ethyl benzene.