Abstract
Biochars have been proposed for remediation of metal-contaminated water due to their low cost, high surface area and high sorption capacity for metals. However, there is a lack of understanding over how feedstock material and pyrolysis conditions contribute to the metal sorption capacity of biochar. We produced biochars from 10 different organic materials by pyrolysing at 450 °C and a further 10 biochars from cedar wood by pyrolysing at 50 °C intervals (250–700 °C). Batch sorption experiments were conducted to derive the maximum Cu and Zn sorption capacity of each biochar. The results revealed an exponential relationship between Cu and Zn sorption capacity and the feedstock C/N ratio and a sigmoidal relationship between the pyrolysis temperature and the maximum Cu and Zn sorption capacity. FTIR analysis revealed that as temperature increased, the abundance of functional groups reduced. We conclude that the high sorption capacity of high temperature biochars is due to an electrostatic attraction between positively charged Cu and Zn ions and delocalised pi-electrons on the greater surface area of these biochars. These findings demonstrate a method for predicting the maximum sorption capacity of a biochar based on the feedstock C/N ratio and the pyrolysis temperature.
Highlights
Metal contamination of surface water by mine water discharged from abandoned metal mines represents an important problem throughout the world due to its impact on freshwater and estuarine ecology and the safety of drinking water (Byrne et al 2012)
The results of this study revealed that the abundance of functional groups on the surface of the biochar decreased with increasing biochar pyrolysis temperature
Cu and Zn sorption capacity increased with increasing biochar pyrolysis temperature and with decreasing biochar feedstock C/N ratio
Summary
Metal contamination of surface water by mine water discharged from abandoned metal mines represents an important problem throughout the world due to its impact on freshwater and estuarine ecology and the safety of drinking water (Byrne et al 2012). Active water treatment technologies such as ion exchange, electro-coagulation, membrane filtration, packed-bed filtration and precipitation have high operation costs and sludge disposal problems (Inyang et al 2012). These disadvantages increase the need to develop passive and low-cost water treatments for Cu and Zn remediation of mine water. Biochar is a carbon-rich material, derived from the pyrolysis of biomass in the absence of oxygen (Beesley et al 2011) It has a high surface area, a considerable negative charge and a strong affinity for cations in water. These properties have led to it being suggested as a potential candidate to remove Cu and Zn from aqueous solutions (Wang et al 2015)
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