Abstract
The adhesion of metal ions from wastewater to surface of a material in an adsorption process had proven to be effective for remediation of wastewater before discharge. There is a growing demand to utilize alternative low-cost adsorbents for the removal of heavy metals from galvanic wastewater in most developing countries. Cow bones are cheap, readily available and can be sourced locally from slaughterhouses and abattoir. Therefore, their use as an alternative adsorbent for remediation of galvanic wastewater had to be assessed. In this study, the efficacy of cow bone char (CBC) was assessed for simultaneous heavy metal ions removal from real life galvanic wastewater in a competitive adsorption process. The galvanic wastewater was characterized using atomic adsorption spectrophotometry while the CBC was characterized using X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR). Batch experiment was performed to determine the effect of adsorbent dose, contact time and agitation speed on the removal efficiency of heavy metal ions from the galvanized wastewater. The concentrations of Mn2+, Fe2+, Zn2+, Pb2+ and Cr2+ in the raw wastewater exceeded the WHO and EPA standards. The adsorbent revealed a significant distribution of well-developed porous, rough surfaces with cracks characterized by different functional groups for the efficient adsorption process. The optimum adsorbent dose for all the metal ions was 0.04 g/100 mL at an optimum contact time of 60 minutes except for Fe2+ with optimum contact time of 20 minutes, and agitation speed of 150 rpm. The maximum metal removal efficiencies obtained for Mn2+, Fe2+, Zn2+, Pb2+ and Cr2were 99.7%, 100%, 99%, 90% and 85% +, respectively. The average adsorption capacity for Mn2+, Fe2+, Zn2+, Pb2+ and Cr2+were 0.44 mg/g, 26.7 mg/g, 78.5 mg/g, 0.133 mg/g for and 10.36 mg/g, respectively. CBC offers efficient and cost-effective removal of selected metal ions from galvanized wastewater.
Highlights
Galvanized wastewater is one of the highly rated toxic wastewater because of its heavy metal contents, organic substances and surfactants, and can be considered among the most polluting wastewater difficult to treat
Characterization of the cow bone char was performed in accordance to procedures outlined in the Association of Official Analytical Chemist (AOAC) [24]
Heavy metal content of the galvanized wastewater The mean concentrations of Mn2+, Pb2+, Zn2+, Fe2+ and Cr2+ in the raw galvanic wastewater are presented in Table 1 against the World Health Organization (WHO) and Environmental Protection Agency (EPA) standards
Summary
All the chemicals and reagents used were of analytical grade. The experiments were performed followin g standard method procedures. Characterization of the cow bone char was performed in accordance to procedures outlined in the Association of Official Analytical Chemist (AOAC) [24]. Contact time effect was performed using six conical flasks with 100 mL of the galvanized wastewater to which 0.02 g of adsorbent was added into each. The flasks were placed in a mechanical shaker and agitated at 150 rpm for different selected contact times of 20, 40, 60, 80, 100 and 120 minutes. Effect of agitation rate was performed to determine its effect on the treatment process, 0.02 g each of the adsorbent was added to 4 conical flasks of 100 mL of the galvanized wastewater. The conical flasks were placed in a mechanical shaker in turns and rotated at the selected speed ranging from 50 to 200 rpm at intervals of 50 rpm at a constant time of 60 minutes.
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