Study On The Adsorption Performance Of Straw Biochar To Cd²⁺ In Water Under Different Conditions

With the rapid development of industrialization and economy in China,a large number of heavy metal pollutants are discharged into the water,resulting in more and more serious ecological problems of water environment.Although the traditional treatment methods such as chemical and physical methods used in the past can achieve the purpose of removing heavy metals to a certain extent,such methods are not only costly,but also have limited ability to remove heavy metals.Not only that,chemical and physical treatment process will be accompanied by secondary pollution,and subsequent disposal for a large number of chemical sludge is also a very difficult problem.Therefore,the adsorption of heavy metals with high cost-effective adsorbents is a hot topic in recent years.Rice straw and corn straw contain a lot of cellulose,rich carboxyl,hydroxyl and other functional groups,which can be made into biochar with strong adsorption capacity for heavy metals.Because of the cold winter in the north of China,if straw is returned to the field,it can not be successfully transformed into friendly substances for soil by microorganisms.It is a good application direction to use the straw to make adsorbents for the treatment of these crop residues.Therefore,in this paper,the rice straw and corn straw from the north were selected to prepare biochar,and its porous structure,a large number of surface functional groups and considerable specific surface area were used to achieve the adsorption of heavy metals.In this paper,rice straw and com straw were selected as raw materials to prepare biochar by pyrolysis,and the adsorption effect and mechanism were studied.The main research contents and results of this paper are as follows:(1)Using rice straw and corn straw as raw materials,biochar was prepared at different pyrolysis temperatures(300?,400 ? and 500?),and characterized by thermogravimetry,mass spectrometry and SEM scanning electron microscopy.The results showed that the carbon content of biochar of rice straw and corn straw decreased with the increase of temperature;the specific surface area and total pore volume of rice straw and corn straw increased with the increase of temperature,and the pH value increased with the increase of temperature;the surface morphology of rice straw and com straw increased with the increase of temperature At the same time,the increase of temperature also makes the cellulose and hemicellulose of rice straw and corn straw slowly pyrolyze,and finally forms the biomass carbon with amorphous structure.Under the conditions of different temperature and raw materials,the removal capacity of heavy metals in aqueous solution was determined,among which the high adsorption capacity of biochar adsorbent was prepared at 400?.(2)The results of single factor experiment showed that:with the initial cadmium ion in aqueous solution as the variable,the adsorption capacity of biomass increased first and then decreased with the increase of cadmium ion content.When the addition amount of biomass carbon was 0.5g and the concentration of cadmium ion was 4 mg/L,the adsorption capacity of biomass carbon reached the best.With the pH of aqueous solution as a variable,the adsorption capacity of biomass carbon increased first and then decreased with the continuous increase of pH.When the pH was 8,the adsorption capacity of biomass carbon reached the best.With the temperature as the variable,the adsorption effect decreases with the temperature rising,and the adsorption effect is the best when the temperature is 15?.With the dosage of adsorbent as a variable,the adsorption rate of cadmium increases rapidly with the addition of carbon,then increases slowly,and then decreases.Therefore,the saturation of adsorption site should be considered in practical application.Taking time as a variable,the adsorption rate slowed down and reached equilibrium at about 40-50 min.(3)According to the isothermal adsorption analysis of the experimental data,the adsorption of biomass carbon to metal ions is more in line with the Langmuir model,which indicates that the adsorption of biomass carbon to cadmium is dominated by single molecule adsorption.At the same time,the 1/n in the Freundlich model fitting data is lower than 0.5,which proves that the adsorption effect is strong and easy to absorb.The conclusion of kinetic model fitting analysis shows that the adsorption of metal ions by biomass carbon is more in line with the quasisecondary kinetic model,which proves that the adsorption of cadmium by biomass carbon is mainly chemical adsorption.(4)Based on the comprehensive analysis of the experimental results,it is concluded that the adsorption performance of corn straw biomass charcoal in cadmium is slightly better than that of rice biochar,and both of them have good capacity to deal with heavy metal pollution.