Study Of The Removal Of Arsenic And Antimony From Water By Chinese Medicine Residue Biochar Loaded Titanium Dioxide

As a new kind of waste recycling adsorption material,biochar is widely used in the remediation of heavy metal pollution in water.However,biochar is difficult to achieve the remediation of complex polluted water due to its physical and chemical properties.The composite biochar prepared by metal/metal oxide loading method combines the advantages of metal/metal oxide and biochar,significantly improving the possibility of simultaneous adsorption of multiple heavy metal pollutants.TiO₂ is widely used for adsorption of arsenic（As）and antimony（Sb）,which can convert highly toxic As（III）and Sb（III）into relatively less toxic As（V）and Sb（V）,and improve the removal effect of arsenic and antimony.In this study,traditional Chinese medicine residue waste was used as the raw material for the preparation of biochar,and Chinese medicine residue biochar loaded titanium dioxide was prepared by a simple sol-gel method.The coupling mechanism of adsorption between the composite and multivalent metalloid elements of arsenic and antimony in water was systematically studied.As the raw material for the preparation of biochar,Chinese medicine residue is different from the general agricultural and forestry wastes such as branches,straws and husks.The internal structure and chemical components of biomass from Chinese medicine residue will be changed by the extraction of Chinese medicine.In order to explain the impact of this change on adsorption performance,this paper took acanthopanax senticosus as an example to deeply explore the mechanism of the influence of the extraction process of Chinese medicine on the physicochemical properties of acanthopanax senticosus residues,acanthopanax senticosus residues biochar and their modified composite materials,as well as the adsorption performance of arsenic and antimony.The research results further deepened the understanding of the adsorption mechanism of titanium dioxide and its composite adsorption materials for simultaneous removal of arsenic and antimony in wastewater,opening up a new way for the resource utilization of traditional Chinese medicine waste residue,and providing scientific reference for the synchronous and efficient remediation of arsenic and antimony composite pollution in antimony mine wastewater.The main research work and results of this paper were summarized as follows:During the process of decocting and extracting,the precipitation of inorganic components and medicinal active organic compounds resulted in an increase in volatile and ash content,a decrease in fixed carbon,an increase in p H,and an increase in specific surface area and total pore volume of acanthopanax senticosus residue.The precipitation of more volatile components during the pyrolysis process was help to improve the pore structure of acanthopanax senticosus residue biochar and increase its specific surface area.Compared with acanthopanax senticosus biomass CW,acanthopanax senticosus medicinal residue JCW,and acanthopanax senticosus biochar CW450,the combined effects of decocting,extracting,and pyrolysis to carbon promoted the optimal pore structure,maximum specific surface area,and optimal adsorption performance of acanthopanax senticosus medicinal residue biochar JCW450.The loading of titanium oxide significantly improved the physicochemical properties of composite materials and provided a large number of active sites for the adsorption of arsenic and antimony.The adsorption performance of composite materials mainly depended on the loading of titanium dioxide.However,the physicochemical properties of the matrix determined the differences in the chemical composition,titanium oxide distribution,pore structure characteristics,and adsorption properties of composite materials.The combined effects of decocting,extracting,and pyrolysis to form carbon promoted a more uniform distribution of titanium oxides on the matrix material JCW450,resulting in the optimal pore structure,maximum specific surface area,and optimal adsorption performance of the loaded modified Chinese medicine residue biochar composite material TJCW450-2.The loading modification greatly improved the adsorption performance of arsenic and antimony on Chinese medicine residue biochar.Considering the removal effect and cost factors,the best composite adsorbent was Tad450-2.The optimum conditions for the preparation of Tad450-2 were carbonization temperature of 450℃,the addition of butyl titanate was the ratio of the volume of butyl titanate to the mass of biochar=2 m L/g.The average pore diameter of Tad450-2 changed from 20.4847 nm to 2.6798 nm,the specific surface area increased by 27.9 times,the total pore volume increased by 3.7 times,the micropore volume increased by 39.1 times,and Zero potential（p Hpzc）incresed from2.30 to 4.40.A large number of TiO₂ nanoparticles were supported on the surface of Chinese medicine residue biochar and existed as anatase.The main exposed crystal surface of titanium dioxide was{101}.The adsorption of arsenic and antimony by this material had the characteristics of wide p H range,strong selectivity and anti-interference ability.Considering the treatment cost and the removal effect of arsenic and antimony,the optimal dosage of composite adsorbent Tad450-2 was the ratio of adsorbent dosage to solution volume=2 mg/m L when concentration of pollutants was 20 mg/L.The adsorption kinetics of single arsenic or antimony on Tad450-2 was more suitable to be explained by the pseudo-second-order model（PSO）.The Sips maximum adsorption capacity of arsenic was 58.456 mg/g at 25℃.The Langmuir maximum adsorption capacity of antimony was 136.159 mg/g at 35℃.The removal of As（Ⅲ）and Sb（Ⅲ）by Tad450-2 was a coupling process of adsorption and photocatalytic oxidation.Tad450-2efficiently removed As（Ⅲ）and Sb（Ⅲ）under dark conditions,indicating that Tad450-2could directly adsorb a large amount of As（Ⅲ）and Sb（Ⅲ）.Light could effectively promote the oxidation of As（Ⅲ）and Sb（Ⅲ）and improve the removal efficiency of pollutants.Superoxide radical(O₂^·-)dominated the oxidation of As（III）.The photocatalytic oxidation of Sb（Ⅲ）by Tad450-2 was affected by hydroxyl radical（（?）OH）and superoxide radical(O₂^·-).And（?）OH was the main oxidant.The mechanism of As（Ⅲ）and Sb（Ⅲ）removal by Tad450-2 was mainly related to Ti-OH group.Arsenic and antimony were immobilized on the composite by complexing with the active site Ti-OH loaded on Tad450-2.In addition,the adsorption of arsenic and antimony by Tad450-2 was also related to its specific surface area,the electrostatic adsorption between the composite materials and pentavalent arsenic oxide anions.In the static adsorption of binary heavy metal system,the coupling effect of arsenic and antimony showed the competition and antagonism of adsorption sites,which significantly affected the removal efficiency of Tad450-2 for pollutants,and the degree of influence was closely related to the concentration of pollutants.The higher concentration,the more obvious competitive adsorption of arsenic and antimony.Antimony had strong competitiveness in the adsorption process,especially when the concentration of pollutants was high.Tad450-2 had strong selectivity and anti-ion interference ability for the removal of arsenic and antimony in the coexistence system.In dynamic adsorption,low pollutant concentration,low influent flow and increased dosage of adsorbent were beneficial to pollutant removal.In the series dynamic adsorption,with the increase of the number of adsorption columns,the time for the arsenic and antimony concentration in the effluent to meet the discharge standard obviously extended,the amount of treated water increased significantly,and the removal rate of arsenic and antimony also increased gradually.When the series adsorption column ran to 11810 min,the removal rates of arsenic and antimony reached 69.40%and 93.76%respectively.Tad450-2 was an economic,efficient and environmentally friendly adsorbent for arsenic and antimony.Tad450-2 had good reusability and stability,which could achieve efficient and simultaneous removal of arsenic and antimony in wastewater.In the dynamic adsorption of binary heavy metal system,the simultaneous removal mechanism of arsenic and antimony included the direct adsorption of As（Ⅲ）and Sb（Ⅲ）,the photocatalytic oxidation adsorption of As（Ⅲ）and Sb（Ⅲ）,and their preemptive and antagonistic effects on the adsorbent sites.In addition to preempting active sites and antagonistic effects,there may also be other interactions between arsenic and antimony in dynamic adsorption.