Influences of pH, heavy metals and phosphate and their co-influences on the sorption of pentachlorophenol on cyanobacterial biomass

Abstract

Influences of pH, two types of ions of transition metals (Cu2+, Cd2+), Na3PO4 and their co-influences on the sorption of pentachlorophenol (PCP) on cyanobacterial biomass derived from natural bloom were studied. Sorption of PCP significantly decreases with pH in the range of 3.25–9.00. Although sorption coefficient of ionized PCP is 8.51 times lower than that of neutral species, it is the dominant species at environmentally relevant pH and contributes more to the total sorption of PCP. In the presence of low concentration of Cu2+ (≤40 μmol L−1), sorption of PCP was much lower than that of the blank. However, it increased gradually with Cu2+, and overpassed the blank when concentration of Cu2+ was higher than 50 μmol L−1. Compared with the sole influence of pH, coexisted Cu2+ inhibited the sorption of PCP at pH of 3.25 and 4.35, but enhanced it in the pH range of 5.00–9.00. In the presence of Cd2+, sorption of PCP first increased then decreased rapidly and finally increased slightly again with Cd2+. Except for at pH of 9.00, sorption of PCP at other pH in the presence of Cd2+ was much lower than that solely affected by pH. In the presence of Na3PO4, sorption of PCP increased rapidly then maintained with Na3PO4. Under the influence of both Na3PO4 and pH, sorption of PCP at pH from 3.25 to 5.00 was lower than that solely affected by pH, while it increased with pH in the range of 5.00–9.00 and was higher than that solely affected by pH in the range of 6.00–9.00. Ion pairs of pentachlorophenolate-metal facilitated the sorption of PCP, which was largely dependent on pH illustrated by UV–visible and FTIR spectra. Speciations of metals and PCP and the stability constants of ion pairs of pentachlorophenolate-metal greatly affected the sorption. Ionic strength also played an important role for the sorption of PCP.