Application of sulphate and magnesium enriched waste rapeseed cake biochar for recovery of Cu(II) and Zn(II) from industrial wastewater generated in sulphuric acid plants

The development of an efficient and green adsorbent is of great significance for copper(II) and zinc(II) removal and recovery from industrial wastewater. In this study, for the first time, waste rapeseed cake is used as a biosource to synthesize MgO-SO3 enriched biochar. The newly developed adsorbent was produced in a one-step process by pyrolysis at 973.15 K for 2 h, under anoxic conditions. Porous structure, specific surface area, and composition of biochar were studied. Furthermore, sorption properties of the obtained biochar in relation to copper(II), zinc(II), and arsenic(III) ions were also studied. The impact of parameters such as: sorption time, temperature, adsorbate concentration, sorbent mass, and solution pH on the efficiency of the adsorption process of the studied cations was examined. Rapeseed cake biochar exhibits good Cu(II) adsorption capacity (90.4 mg g-1) with a short equilibrium time (4 h), which indicates the competitiveness to similar adsorbents. The adsorption of Cu(II) on the biochar was more consistent with the pseudo-second-order kinetic models and Langmuir model. The Freundlich and pseudo-second-order kinetic models best fitted the removal of Zn(II) by modified biochar. The mechanism of Cu(II) and Zn(II) adsorption was also postulated. Experimental data collected have shown that the presence of arsenic(III) at higher concentrations adversely affects the sorption efficiency of Cu(II) and Zn(II) ions. Thus, this study shows that the sorbent can be successfully used for the separation of Cu(II) and Zn(II) from technological wastewaters. A flowsheet for the proposed process is presented.