From waste to eco materials – the application of sour cherry stone sorbents in heavy metal removal

Abstract

Serious environmental problem worldwide are effluent waters from many industries, such as mining, refining ores, pesticide, batteries, paper industries, etc., containing toxic components, mostly heavy metals, which are not treated properly in many cases. These pollutants pose serious threat to environment and human health because of their toxicity, persistence and bioaccumulation tendency. There are plenty of conventional methods for heavy metal removal, but in most cases, they are too expensive for removing low, but still toxic present concentrations, with high operational cost/energy demand, or they create large quantities of toxic sludge which request further processing. The application of low cost, mostly waste materials as a heavy metal sorbent are a potential alternative to the existing conventional technologies for the removal/recovery of metal ions from aqueous solutions. The major advantages of sorption by renewable biomass over conventional treatment methods include low cost and abundance of biomaterials, high efficiency with minimum sorbent treatments, minimization of sludge generation and feasible regeneration with possibility of metal recovery. At the same time, application of renewable waste materials contributes to carbon sequestering and climate change mitigations, avoiding land usage and negative impact of landfilled material onto environment. The revalorization of this kind of sorbents also contributes to resource conservation and circular economy in its broadest sense. In this research, lignocellulosic waste material from food industry (sour cherry stones) has been applied as a sorbent for treatment of polluted water with various heavy metals. The sour cherry stones are widespread, locally available waste with considerable potential for sorbents development. This lignocellulosic material was grinded into particle size of approximately 0.5 mm, marked as CSP, and investigated for removal of heavy metal content in contaminated water containing highly toxic metals: Cd2+, Cu2+, Ni2+, Zn2+, and Pb2+. Sorption experiments were performed in an isothermal batch system with stirring under specified operational conditions, avoiding metal precipitation. The removal efficiency of investigated metals reduced in order Pb2+ > Cd2+ > Cu2+ > Zn2+ > Ni2+ using CSP as a sorbent. The CSP characterisation included: contact pH (pHsus), point of zero charge (pHpzc), Scanning Electron Microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Structural characterization of the CSP surface was performed using Fourier transform infrared spectroscopy (FTIR), which disclosed the presence of specific functional groups (hydroxyl, carbonyl and carboxyl) responsible for the removal of heavy metals ions. The obtained results suggest that the application of the raw CSP is an economic and environment feasible strategy for removing heavy metals from water polluted streams.