Adsorptive Removal of Copper Ions from Polluted Water Using Sorbents Derived from Cordia dichotoma, Albizia thompsonii and Polyalthia cerasoides Plants

Abstract

Three different activated carbons as effective adsorbents were prepared by digesting the stems of Cordia dichotoma, Albizia thompsonii and Polyalthia cerasoides plants in conc. H2SO4 for Cu2+ removal from wastewater. The sorption natures of these sorbents are optimized with respect to various physico-chemical characteristics for the maximum Cu2+ removal using simulated waters. Cordia dichotoma (CDAC), Albizia thompsonii (ATAC) and Polyalthia cerasoides (PCAC) activated carbons show good sorption capacities of values: 97.0, 76.8 and 66.7 mg/g, respectively in a wide pH ranges. Unlike that of other two activated carbons, Cordia dichotoma activated carbon is effective even in acid conditions, indicting its direct applicability to Cu-based industrial effluents which are generally acidic in nature. Interference of two fold excess of co-ions is minimal. The established extraction conditions for the removal of more than 95.0% from 10 ppm Cu2+ solution at room temperature (303 K) using CDAC as sorbent are: pH: 3-9; time of equilibration: 1 h; sorbent dosage: 0.100 g/100 mL; with ATAC: pH: 6-9; time of equilibration: 1.5 h and sorbent dosage: 0.125 g/100 mL; and with PCAC: pH: 6-9; time of equilibration: 2.0 h and sorbent dosage 0.50 g/100 mL. Spent adsorbents can be regenerated and reused until four cycles with minimal loss of adoption capacities. Thermodynamic studies revealed that the sorption is spontaneous and endothermic in nature. Further, the ΔH value for CDAC is 30.156 KJ/mol; it indicates the strong chemisorption and may be through reduction to Cu+/Cu and/or complex formation between Cu2+ and functional groups of the adsorbent. The ΔH values of other two activated carbons, ATAC and PCAC, indicated that the sorption is mainly physical with strong inclination towards chemical nature. Positive ΔS values of all the three sorbents, emphasizes the disorder or randomness at the solid-liquid interface and hence favourable conditions for more penetration of Cu2+ into the surface layers of the adsorbent and hence, more removal of Cu2+ ions. The negative ΔG values indicate that the sorption forces are good enough to cross the potential barrier at the solid-liquid interface and hence the process is spontaneous. The prepared three activated carbons were also successfully applied to industrial effluent and polluted lake samples.