Arsenic adsorption on two types of powdered and beaded coal mine drainage sludge adsorbent

The aim of this study was to evaluate the performance of a new adsorbent in terms of beading the sludge generated from coal mine drainage or arsenic removed from water is treated by electro-purification (EP) and chemical-precipitation (CP) methods. Batch experiments were conducted to study the influence of experimental parameters such as pH and temperature, as well as the mechanism of arsenic adsorption with the new adsorbent. The porosity of coal mine drainage sludge (CMDS)-beaded adsorbent made of chitosan and alginate was optimized by adding NaHCO₃ powder to generate CO₂ gas during the preparation process. Two types of adsorbents, beaded EP Najeon CMDS (BCMDS_EP-NJ) and beaded CP Yeongdong CMDS (BCMDS_CP-YD), were prepared by heating. The specific surface areas of the powdered adsorbents CMDS_EP-NJ and CMDS_CP-YD were 104 and 231 m² g^-1, respectively. The prepared beaded adsorbents BCMDS_EP-NJ and BCMDS_CP-YD had good porosity and specific surface areas of 16.8 and 21.2 m² g^-1, respectively. The X-ray diffraction results showed that the structure was goethite (aragonite) and schwertmannite. The pseudo second-order, intra-particle, and Langmuir models were used to explain the adsorption process. The q_max values of As(III) with BCDMS_EP-NJ and BCMDS_CP-YD adsorbents are 4.31 and 4.58 mg g^-1, respectively and those of AS(V) are 9.31 and 10.93 mg g^-1, respectively. The adsorption capacity for As(III) increased with increasing pH, whereas that for As(V) decreased. The activation energy was 8 kJ mol^-1 or more. The mechanism of adsorption of arsenic using a beaded adsorbent was chemical adsorption followed by diffusion. The results of the present study suggest that new adsorbents can be effectively utilized for arsenic removal from water.