Humified insoluble solid for efficient decontamination of nickel and lead in industrial effluents

•The residual solid obtained from a vermicompost retains Ni2+ and Pb2+.•Ionizable structures favor interactions with the cations of heavy metals.•HIS retains Ni2+ and Pb2+Qmax of 34.1 mg g−1 (HIS) and 151.1 mg g−1 (HIS), respectively.•HIS efficiency was 98% and 96% retention of Ni2+ and Pb2+ from wastewater.

The aim of the present study was to evaluate the ability to retain heavy metals cations (Ni2+ and Pb2+) from humified insoluble solid (HIS) that remains after the humic substances (HS) are extracted from a vermicompost (VC) in industrial wastewaters. HIS has ionizable functional groups and carbon types belonging to oxygen structures (di-OAlkylC, OAromatic, COOH, CO) with potential to establish interactions with heavy metals cations in aqueous dissolution. The kinetic study showed a pseudo-second-order behavior of retention, and the adsorption was best described when data were analyzed using the Freundlich isotherm. The Qmax for Ni2+ and Pb2+ was 34.1 mg g−1 (HIS) and 151.1 mg g−1 (HIS). Scanning electron microscopy (SEM) confirmed the retention of heavy metals on the HIS surface; additionally, the spectra of HIS with retained metals indicated the involvement of the oxygen groups in the interaction with metals. The effectiveness of HIS to retain Ni2+ and Pb2+ was determined in retention studies with industrial effluents in lab conditions with 5 g, 10 g and 20 g, pH 7, contact time: 150 min and T = 25 °C. Tests made with industrials wastewater “Factory of White Ceramic” showed that the extraction capability of Ni2+ and Pb2+ was 98% and 96%, respectively. These results demonstrate for the first time, the ability of the (HIS) material to be used as remover of heavy metal cations.

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