Adsorption of arsenic from micro-polluted water by an innovative coal-based mesoporous activated carbon in the presence of co-existing ions

• New carbon (M-NCPAC) with well-developed porosity was prepared by a novel procedure.
• M-NCPAC was a promising adsorbent with high adsorption capacities for arsenic ions.
• Presence of chromium species resulted in decreasing of arsenic adsorption capacities.
• Phosphate competed more strongly with As(III) than with As(V).
• Competition between arsenic and co-existing anion was lower in Arsenic-Cr(VI) system.

A novel, multi-step procedure was introduced to prepare an innovative coal-based activated carbon (M-NCPAC) in the present work. The adsorption characteristics of As(III)/As(V) ions in low concentrations (0.5 mg/L) from an As(III)/As(V) system were studied at 4 °C. The effects of co-existing Cr(VI) on arsenic adsorption by M-NCPAC were also determined as a function of pH, contact time and adsorbent dose in an arsenic-Cr(VI) system. The results suggested that M-NCPAC has well-developed porosity and absorption ability, such as high pore volume (1.1495 cm3/g), mesoporosity (64.22%), iodine numbers (1137 mg/g), and methylene blue (244 mg/g). The optimum pH for arsenic adsorption was identified as 6. M-NCPAC was proven to be a promising adsorbent (Qm,As(III) = 1.634 mg/g, Qm,As(V) = 1.701 mg/g) in the As(III)/As(V) system. Arsenic adsorption was suppressed in the arsenic-Cr(VI) system, and Qm,As(III) and Qm,As(V) at the optimum pH decreased by 18.23% and 11.06%, respectively. Arsenic adsorption on M-NCPAC in different systems obeyed the pseudo-second-order equation. The effects of four anions on arsenic adsorption were also evaluated either in an As(III)/As(V) system or in an arsenic-Cr(VI) system. The degrees of influence on arsenic adsorption decreased in the following order: phosphate > silicate > carbonate > sulfate. However, chromium species lowered the competitive adsorption between arsenic species and co-existing anions in the arsenic-Cr(VI) system.