Removal Of Chromium And Manganese From Water By Dithiocarboxyl Chitosan Performance And Research

The treatment of heavy metal wastewater has always been an important part of the environmental management of water bodies,and its pollution has caused very serious harm to the water environment and human health due to its harmful and continuous nature.21 st century,people pay more and more attention to the treatment of water pollution,and the treatment methods are gradually changing from the traditional sewage treatment methods to a greener and more environmentally friendly and harmless direction.In this work,in order to provide new ideas for the subsequent treatment of heavy metal wastewater,a heavy metal flocculant,prepared by using chitosan and named dithiocarboxyl chitosan(DTCTS),was selected to study its performance on the removal of heavy metals chromium and manganese under different conditions,and its removal mechanism was explored.In this paper,the heavy metal simulated wastewaters containing Cr(VI)and Mn(VII)were used as the test object,and DTCTS was used as the heavy metal flocculant,focusing on its removal effect on heavy metals under common water quality conditions,and the chelating ability of DTCTS on heavy metals under the influence of different coexisting substances.Furthermore,the removal mechanisms of chromium and manganese by DTCTS were explored.The experimental results were as follows:(1)The optimum dosage of DTCTS for the removal of Cr and Mn was 660 mg/L and120 mg/L,and the removal rates reached 97.3% and 99.0%,respectively.The chelating flocs for heavy metal after the experiment showed yellowish green and dark brown,respectively,and all of them could finish settling within 20 min,and the liquid supernatant was clear and transparent.(2)The optimal hydraulic flocculation conditions for the removal of Cr(VI)by DTCTS were fast stirring speed of 140 r/min,fast stirring time of 2.5 min,slow stirring speed of 40r/min,slow stirring time of 20 min.The optimal hydraulic flocculation conditions for the removal of Mn(VII)by DTCTS were fast stirring speed of 180 r/min,fast stirring time of 2.5min,slow stirring speed of 40 r/min,slow stirring time of 20 min.(3)For water samples containing Cr(VI),the best removal efficiency could be achieved when the initial p H of the system was 2.5,and the removal rate of both Cr(VI)and total chromium could reach more than 95% under a certain dosage.For water samples containing Mn(VII),the best removal efficiency could be achieved when the initial p H of the system was4.0,and the highest removal rate of Mn could 99.6%.(4)When the initial concentrations of Cr(VI)and Mn(VII)were different,DTCTS had a good removal efficiency on them,and the removal rate could finally reach more than 97.0%.The chelating flocs formed after the flocculation experiment increased with the increase of the initial concentration of heavy metal ions.(5)When some inorganic substances(anions/cations)and organic substances existed in the system,a certain inhibitory effect on the removal of chromium and manganese was showed,but the presence of some ions could promote the removal of Cr(VI)and Mn(VII).However,the inhibitory/promoting effect could be weakened or even disappeared with the increase of DTCTS dosage.When turbidity existed in the system,it also had a certain inhibition effect on the removal of heavy metal ions,and the inhibitory effect decreased with the increase of DTCTS dosage;meanwhile,the turbidity in the system decreased.This indicated that DTCTS had the dual functions of heavy metal chelation and turbidity removal.(6)The Fourier infrared analysis and scanning electron microscopy-energy spectroscopy analysis showed that DTCTS had the effects both redox and chelating flocculation on heavy metals chromium and manganese,and the dithiocarbonyl group on the macromolecule chain of DTCTS mainly played the role of redox,and the amino group in the solution also participates in the reaction;also,there may be part of the ion exchange effect.In conclusion,heavy metal flocculant dithiocarboxyl chitosan(DTCTS)can efficiently trap and remove chromium and manganese from water,and has good application prospects in actual wastewater.