Effects of chemical aging on mineral structure and Pb2+adsorption of Mg-modified biochar
The aim of this study was to explore effects of aging time on the properties of metal-modified biochar and its immobilization effect on heavy metals.Biochar impregnated with MgCl2 was subjected to a six-month aging test using a non-biochemical aging method at constant temperature(60℃and 90℃)and humidity(40%).The FT-IR showed that the aging process enabled the introduction of oxygen-containing functional groups,such as—COOH and C=O,on the surface of the biochar,thus enhancing the Pb2+-chelating ability of the biochar.Zeta potential results indicated that aging further improved the electronegativity of the biochar,because the functional groups on the surface(such as—OH)were oxidized to—COOH during the aging process.In addition,the Langmuir model was found to be the most appropriate to describe the biochar after Mg modification and aging,based on the adsorption isotherm results.After aging at 60℃,the specific surface area of Mg-modified biochar was approximately 22 times that of freshly made modified biochar.This was because the mineral morphology changed during the aging process,forming magnesium oxide with a porous structure.Therefore,after aging at 60℃,the Pb2+-adsorbing capacity of Mg-modified biochars prepared at 500℃and 700℃increased by 54.4%and 67.4%,respectively.However,after aging at 90℃,Mg-modified biochar produced methyl radicals,which destroy the carbon structure of biochar and reduce the specific surface area.Thus,the heavy metal adsorption capacity of biochar aged at 90℃(48.26 mg∙g-1)was not as high as that of biochar aged at 60℃(62.85 mg∙g-1).Therefore,although the heavy metal adsorption capacity of aged Mg-modified biochar could be improved after a short period of ageing(at 60℃),as the ageing continues(i.e.,temperature increases to 90℃),the microporous structure within the aged Mg-modified biochar was ultimately converted into amorphous minerals,this resulted in a significant reduction in the Pb2+-adsorbing capacity of the biochar.
abiotic agingpore structureMg-modified willow biocharheavy metal fixationmineral morphology
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