Magnetic biochar derived from sewage sludge of concentrated natural rubber latex (CNRL) for the removal of Al3+ and Cu2+ ions from wastewater

Abstract

In order to reduce sewage sludge of concentrated natural rubber latex (CNRL) and transform it into a valuable material for efficient removal of Al3+ and Cu2+ ions from wastewater, magnetic biochar was prepared. In this work, sewage sludge from CNRL was pyrolyzed at various temperatures (300–700 °C) to assess the effects of pyrolysis temperature on the efficiency of magnetic biochar in removing Al3+ and Cu2+ ions from an aqueous medium. Effect of the chemical composition of sewage sludge on the biochar characteristic was evaluated. Sewage sludge is mainly organic matter. The mineral elements silicon (Si), phosphorus (P), sulfur (S) and calcium (Ca) were also observed in the sewage sludge. With increasing pyrolysis temperature, the contents of P and potassium (K) increased. The inorganic metals chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni) and lead (Pb) were present in small quantities. Pyrolysis temperatures 400–500 °C provided good quality magnetic biochar, while with the higher 700 °C pyrolysis temperature, specific surface area and pore volume decreased. The prepared biochar had combined meso- and macro-porous structure. Isotherms of Type II were indicating multilayer adsorption on porous biochar. The pseudo-second-order kinetic models described well Al3+ and Cu2+ adsorption onto magnetic biochar. The leaching test of magnetic biochar shows the releasing of K and Zinc (Zn) which can effect on the sorption of Al3+ and Cu2+. The binding mechanism between magnetic biochar and Al3+/Cu2+ involved surface complexation, ion exchange and cation‒π interaction.