Abstract
The influence of pyrolysis temperature on cadmium (Cd) removal capacity and mechanisms by maize straw biochars (MSB) and Platanus leaves biochars (PLB) pyrolyzed at 300, 400, 500 and 600 °C was investigated. The results showed that the biochars pyrolyzed at 500 °C had the highest adsorption capacity for Cd, and the maximum adsorption at pH 5.0 was 35.46 mg/g and 25.45 mg/g for MSB and PLB, respectively. The increase in adsorption efficiency with increasing temperature indicated that the adsorption of Cd onto the biochars was endothermic. Based on the balance analysis between cations (Ca2+ and Mg2+) released and Cd adsorbed onto biochar in combination with SEM-EDX, FTIR, and XRD analysis, it was concluded that cation exchange, complexation with surface functional groups, precipitation with minerals (CdCO3), and coordination with π electrons were the dominant mechanisms responsible for Cd adsorption by MSB. With the pyrolysis temperature increasing from 300 to 600 °C, the contribution of cation exchange (Ca2+ and Mg2+) on Cd removal by MSB decreased from 37.4% to 11.7%, while the contribution of precipitation with Otavite (CdCO3) and Cd2+-π electrons interaction increased. For PLB, the insoluble Cd minerals were not detected by XRD, and the contribution of cation exchange had no significant difference for PLB pyrolyzed at 300, 400, 500 and 600 °C.
Highlights
Cadmium (Cd) is a highly toxic heavy metal with strong mobility, bioavailability and accumulation, which can cause severe damage to human health
For Platanus leaves biochars (PLB), the insoluble Cd minerals were not detected by X-ray diffraction (XRD), and the contribution of cation exchange had no significant difference for PLB pyrolyzed at 300, 400, 500 and 600 ◦ C
The results concluded that pyrolysis temperature had a great effect on the capacity and mechanism of Cd adsorption on the biochars
Summary
Cadmium (Cd) is a highly toxic heavy metal with strong mobility, bioavailability and accumulation, which can cause severe damage to human health. Many methods including chemical precipitation, ion exchange, adsorption and membrane separation have been developed to remove cadmium from wastewater. Many adsorbents have been successfully used for the removal of Cd from wastewater, including commercial activated carbon, clay minerals, biomass and agricultural waste [1]. Adsorption by using low-cost materials is considered as one of the most efficient methods to remove cadmium from wastewater due to its high efficiency, low cost and environmentally friendly nature [2]. A carbon-rich material, has been successfully used for carbon sink, climate change mitigation and soil remediation [3,4,5]. Biochar has been successfully used to remove heavy metal from wastewater, including Cd [6,7,8]. The adsorption capacity and mechanisms of heavy metal adsorption by biochar could be influenced by the properties of biochar, such as surface
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