Preparation Of Composite Adsorbent From Titanium-containing Blast Furnace Slag And Its Cr(VI) Adsorption Performanc

In the process of economic development,the efficient production and operation of various large enterprises and factories and the irregular discharge of industrial wastewater cause extensive pollution of rivers.Heavy metal pollution problems are becoming increasingly prominent.Hexavalent chromium Cr（VI）,as one of the mo st toxic heavy metals,has largely affected the healthy growth of animals and plants and humans.Titanium-containing blast furnace slag is a solid waste product produced in the blast furnace smelting process of vanadium and titanium magnetite.The large accumulation of the slag not only wastes precious land resources,but also poses a serious threat to the surrounding environment.Recycling of titanium-containing blast furnace slag,from which chromium adsorbent was prepared,not only achieved the secondary use of smelting slag,but also solved the problem of excessive levels of hexavalent chromium in the water environment.In this paper,a low-cost and high-removal rate Cr（VI）adsorbent（GLZ-jcz/CS）was prepared by crosslinking glutaraldehyde and compositing chitosan with stable leaching slag matrix material（GLZ-jcz）obtained by leaching titanium-containing blast furnace slag with nitric acid.The titanium-containing blast furnace slag,th e leaching slag matrix before and after modification and the adsorbent before and after adsorption were characterized and analyzed.The effects of acid leaching process,recombination process and adsorption of Cr（VI）on the chromium removal performance of G LZ-jcz/CS adsorbent were explored,and finally the adsorption kinetics and isotherm model fitting of GLZ-jcz/CS adsorbent in Cr（VI）-containing solution were investigated,and the mechanism and regeneration performance of Cr（VI）removal of GLZ-jcz/CS adsorbent were briefly analyzed.（1）Titanium-containing blast furnace slag is an amorphous substance with uneven particle size,mainly composed of oxides such as silica and titanium dioxide.The nitric acid solution was used to leach titanium-containing blast furnace slag to prepare the leaching slag matrix material by separating calcium and magnesium from the raw material,and experimental studies showed that the optimum test conditions for the acid leaching process were:the solid ratio of nitric acid solution to slag liquid is 9:1,the mass concentration of nitric acid is 14%,the stirring speed is 400 r/min,the reaction time is 120 min,and the reaction temperature is 75°C,the adsorption rate of GLZ-jcz/CS adsorbent on hexavalent chromium in simulated waste water was81.66%.（2）The modification process of glutaraldehyde crosslinked composite chitosan on GLZ-jcz matrix materials was studied,and the optimal test conditions were obtained:The composite temperature of chitosan and leaching slag is 45°C,the ratio of chitosan to leaching slag is 1:2,the dropwise addition amount of glutaraldehyde is6.5 ml,and the reaction time after adding leaching slag is 120 min.In which case,the adsorption rate of 50 mg/L Cr（VI）was 81.66%,and the adsorption capacity was40.83 mg/g.The characterization and analysis of GLZ-jcz matrix materials before and after modification showed that the amorphous structure of the leaching slag matrix was not changed after modification;but the N elements are detected in the element mapping diagram.In infrared analysis,the change of amino and hydroxyl vibration peaks proves that hydroxyl groups and amino groups on chitosan participate in recombination,the appearance of C=N bonds proves that the-CHO of glutaraldehyde and the-NH₂ on the surface of the GLZ-jcz/CS adsorbent undergo Schiff base reaction,and indicates that chitosan has been successfully loaded on the leaching slag matrix layer,and glutaraldehyde has been successfully cross-linked.The uniformity of particle size distrib ution of GLZ-jcz matrix material before and after modification was high,and GLZ-jcz/CS showed small specific surface area and total pore volume,which may be due to pore blockage caused by chitosan modification,resulting in partial pore loss during the c rosslinking process.（3）The adsorption process of GLZ-JCZ/CS composite adsorbent on Cr（VI）in simulated chromium-containing wastewater was studied,and the optimal adsorption process conditions were determined as:the adsorption temperature was 70°C,the initial p H value of simulated chromium-containing wastewater was 4,the adsorbent dosage was 0.13 g,the initial concentration of Cr（VI）was 50 mg/L（volume of 100m L）,and the adsorption time was 120 min,in this case,the adsorption rate of Cr（VI）was up to 99.82%.（4）Adsorption kinetic studies showed that the relevant data of GLZ-jcz/CS composite adsorbent in the process of removing Cr（VI）are more in line with the quasi-secondary kinetic model,indicating that the adsorption process is mainly based on chemical adsorption and coordination complexation with chromium.The adsorption isotherm data are more consistent with the Redlich–Peterson adsorption isotherm model,indicating that the GLZ-JCZ/CS adsorbent is a monolayer adsorption on a uniform surface for the simulated adsorption process containing Cr（VI）.In the adsorption experiment,the adsorption capacity of GLZ-JCZ/CS composite adsorbent for Cr（VI）was as high as 185.85mg/g.（5）The adsorption mechanism of GLZ-jcz/CS adsorbent was studied.Combined with the analysis of XPS and FTIR during the adsorption process,it was concluded that the adsorption mechanism of Cr（VI）by GLZ-jcz/CS adsorbent included electrostatic attraction,reduction and coordination complexation.First,Cr（VI）is adsorbed to the surface of the adsorbent by electrostatic attraction,and a part of Cr（VI）is complexed with amino coordination;Part of Cr（VI）is reduced to Cr（III）,Cr（III）forms a hexacoordinated hydrated ion[Cr（H ₂O）₆]³⁺with water,and there are lone pairs electrons in the amino group on the surface of the GLZ-jcz/CS adsorbent,which form covalent bonds with trivalent chromium ion electron holes.（6）The regeneration performance of GLZ-jcz/CS adsorbent was studied.HCl was used as the eluent.After six desorption-adsorption,the adsorption rate of Cr（VI）was as high as 96.22%,and the regeneration rate of GLZ-jcz/CS adsorbent was above96%,which indicated that GLZ-jcz/CS composite adsorbent is a high-potential high-quality adsorbent.