Pentachlorophenol removal from aqueous matrices by sorption with almond shell residues

Abstract

Sorption with activated carbon has been the technique preferred for pentachlorophenol (PCP) removal from contaminated waters, but regeneration needs and high operation costs are supporting a renewed interest in the search for alternative sorbents. Among them, almond shell, an agricultural by-product, provides interesting economical advantages, once shells account for 50% (in mass) of the whole almond. In this work, the capacity of almond shells to remove PCP from waters without previous activation was studied in batch conditions. While PCP analysis was performed solid-phase microextraction (SPME) followed by gas chromatography with electron capture detection (GC-ECD), mercury porosimetry and Fourier transform infrared spectroscopy (FTIR) provided a preliminary physical and chemical characterization of the sorbent. Almond shells were essentially a macroporous material, with an average surface area of 12.9 +/- 2.8 m(2)/g. The efficiency of PCP removal was 93 +/- 14%, in 24 h, with an initial concentration of 100 mu g/l PCP and 5 mu g PCP/g shell. Isotherm data adjusted better to Freundlich equation, where K-F and 1/n were 0.075 +/- 0.081 mg(1-1/n) 1(1/n) and 1.882 +/- 10.289, respectively. Average desorption efficiency was 7%, indicating strong adsorption capacity. Results proved that almond shells may be an excellent low-cost alternative for PCP removal from contaminated waters.