Abstract
In this study walnut shells, an inexpensive and readily available waste, were used as carbonaceous precursor for preparation of an innovative adsorbent (walnut-shell powder (WSP)) which was successfully tested for the removal of FeII from synthetic acid mine drainage (AMD). Then, the exhausted iron-contaminated adsorbent (WSP-FeII) was recovered and treated with sodium borohydride for the reduction of adsorbed FeII to Fe0. The resulting material (WSP-Fe0) was subsequently tested for the removal of CrVI from aqueous solutions. Treatability batch experiments were employed for both FeII and CrVI-contaminated solutions, and the influence of some important experimental parameters was studied. In addition, the experimental data was interpreted by applying three kinetic models and the mechanism of heavy metal removal was discussed. The overall data presented in this study indicated that fresh WSP and WSP-Fe0 can be considered as promising materials for the removal of FeII and CrVI, respectively. Furthermore, the present work clearly showed that water treatment residuals may be converted in upgraded materials, which can be successfully applied in subsequent water treatment processes. This is an example of sustainable and environmentally-friendly solution that may reduce the adverse effects associated with wastes and delay expensive disposal methods such as landfilling or incineration.
Highlights
The present work clearly showed that water treatment residuals may be converted in upgraded materials, which can be successfully applied in subsequent water treatment processes
Much less interest has shown for finding environmentally-friendly solutions for the management of residual solids resulted from such water treatment processes
The present paper presents data on the use of WSP, a local agricultural waste, for the sequential removal of two heavy metals, namely FeII
Summary
Water pollution with heavy metals has become an increasingly important worldwide threat. Numerous heavy metals have been introduced into natural water environments, especially as a result of human industrial activities, and due to agricultural, transport and waste disposal practices. Even heavy metals which are necessary in small amounts as micronutrients for the normal development of biological systems (e.g., Cu, Fe, Zn, Cr etc.) exert harmful effects to biological organisms at high concentrations [4,5,6]. The removal of heavy metals from contaminated waters, prior to their discharge into natural effluents, is a necessary step in order to reduce their adverse effects.
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