Characteristics Of Biochar Production By Invasive Plants In South China And Adsorption Of Cd²⁺ And Cu²⁺ In Water

Invasion of alien plants has become a global ecological environment problem,which poses a serious threat to biodiversity,social and economic development and human health.In the production activities,the discharge of wastewater containing heavy metals causes serious pollution of heavy metals in water.Biochar has attracted extensive attention from researchers at home and abroad because of its rich surface oxygenated functional groups,developed pore structure and high specific surface area.The usage of biochar prepared from invasive plant biomass in the treatment of polluted water can serve as a new way for the resource utilization of invasive plants and waste recycling,and also provide new adsorbents for the treatment of heavy metal polluted water.Based on five invasive plants in South China,bidens pilosa-derived biochar（BBC300、BBC500、BBC700）,eupatorium catarium-derived biochar（EBC300、EBC500、EBC700）,ipomoea cairica-derived biochar（IBC300,IBC500,IBC700）,mikania micrantha-derived biochar（MBC300、MBC500、MBC700）and lantana camara-derived biochar（LBC300,LBC500,LBC700）were prepared under the pyrolysis temperature of300,500,and 700℃,respectively.Physicochemical properties of biochars were determined through elemental analysis,Fourier transform infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）,X-ray diffraction（XRD）and specific surface area（BET）.Adsorption characteristics of Cd²⁺and Cu²⁺in aqueous solution were studied for the selected biochar BBC500,EBC500,IBC500,MBC500 and LBC500.（1）The pyrolysis temperature impacted greatly on the physicochemical properties of biochar made from the five invasive plant biomasses.With the increase in pyrolysis temperature,the yield of the five biochars decreased and ash content（13.35～38.26%）increased;The higher pyrolysis temperature also increased the p H value of the solution（7.97～12.00）and decreased the O/C and H/C ratios.the specific surface area was smaller than that of the LBC700 of 15.82 m²/g;The cation exchange capacity（CEC）of the five invasive plant biomass was enhanced with the increase in temperature.LBC700 has a maximum CEC value of 210.38 cmol/kg;Five invasive plant biochars were found to be rich in oxalate,potassium chloride,carbonate or bicarbonate.The ash content（38.26%）and the p H value（p H=12.00）of MBC700 are relatively high.（2）The adsorption process of the five invasive plant biochars on Cd²⁺and Cu²⁺fitted the Langmuir and Freundlich models.The Langmuir model can better describe the adsorption of Cd²⁺by BBC500 and EBC500,and the adsorption of Cu²⁺by EBC500,IBC500 and MBC500 compared to the Freundlich model.The Freundlich model well describes the adsorption of Cd²⁺by IBC500,MBC500 and LBC500 and the adsorption of Cu²⁺by BBC500 and LBC500.The quasi-secondary kinetic model describes well the adsorption kinetics of Cd²⁺and Cu²⁺in five biochars.Chemical adsorption was main reaction in the removal of Cd²⁺and Cu²⁺.The maximum adsorption of Cd²⁺by five biochars was in the order of BBC500>EBC500>MBC500>IBC500>LBC500.The maximum adsorption of Cu²⁺by five biochars was in the descending order of BBC500,MBC500,IBC500,LBC500,EBC500.Bidens pilosa-derived biochar（BBC500）showed the highest adsorption capacity of Cd²⁺（167.65 mg/g）and Cu²⁺（65.55 mg/g）.Therefore,the bidens pilosa-derived biochar has a great adsorbent potential for the removal of Cd²⁺and Cu²⁺in aqueous solution.