Study On Functional Modification And Adsorption Properties Of Wood Chip Screening Reject

The paper industry uses wood resources as raw materials and consumes a large amount of wood every year.The wood chip screening reject(WCSR),which accounts for about 3%-5%of the raw material,is used as the waste material in the process of pulping and chipping.The WCSR is composed of sawdust and needle.It is difficult to dispose of,but the cost is low and the collection is convenient.Industrial industry is the biggest driving force for the development of a country.With the continuous development of China's economy,the number of processing enterprises and industrial products is increasing.However,with the rapid development of industry,the problem of environmental pollution is becoming more and more serious.The discharge and disposal of industrial wastewater has brought tremendous pressure to the environment.The wastewater containing heavy metal ions has attracted much attention.Heavy metal ions such as chromium,iron,copper and lead in wastewater will accumulate in the environment and organisms,which poses a great threat to the human health.Adsorption and enrichment is the key link and main means of wastewater treatment,but the cost of adsorbent material is the key to restrict the wide application of this technology.WCSR is cheap and convenient collection.Using WCSR as adsorbent to absorb heavy metal ions in wastewater and realize the effective utilization of wastes is an economic and environment treatment method,which conforms to the development model of circular economy and has important significance.In this study,nitric acid,phosphoric acid and sodium hydroxide were used to modify WCSR at room temperature.The effects of three modification methods on WCSR and adsorption of Cr(?)and Fe(?)ions in water were studied and compared.The process of nitric acid modification with better modification effect was optimized.The results showed that the content of cellulose,hemicellulose and lignin of WCSR modified by 1mol/L nitric acid and 1mol/L phosphoric acid decreased to different degrees,and the change of three components of WCSR modified by sodium hydroxide was the smallest.The specific surface area of WCSR could be increased in different degrees by three modification methods,and the room temperature modification treatment was determined by analyzing the changes of specific surface area,pore volume and average pore size.The results of XRD analysis are the same as that of surface modification.SEM analysis showed that there were a large number of pore sizes of about 5 microns on the surface of the WCSR.After modification with nitric acid and phosphoric acid,the pore size increased slightly.FT-IR showed that the surface of WCSR contained functional groups such as hydroxyl groups.After modification,the absorption peak of hydroxyl groups increased in varying degrees.Elemental composition analysis(EDS)was also used to characterize WCSR and modified WCSR.It was found that three modifiers had little effect on the internal element composition of WCSR.The adsorption analysis of iodine and methylene blue showed that the adsorption effect of three kinds of modified WCSR was significantly increased,and the adsorption effect of nitric acid modified WCSR on iodine and methylene blue was the best.Three kinds of modified WCSR were applied to the adsorption of Cr(?)and Fe(?)in simulated wastewater.The removal effects of heavy metal ions in wastewater under different adsorption conditions were discussed.The results showed that the adsorption effect of nitric acid modified WCSR was the best.The removal rate of Cr(?)was the highest when the initial concentration of Cr(?)was 15 mg/L,the dosage of WCSR was 50.00 g/L,the pH value was 2.0,the adsorption temperature was 30 C,and the adsorption time was 80 min,and the removal rate of Cr(?)was 88.64%.The adsorption of Cr(?)by three kinds of modified WCSR conforms to Freundlich isothermal adsorption model and quasi-second-order kinetic model.It was found that nitric acid modified WCSR had the best adsorption effect on Fe(?).When the initial concentration of Fe(?)was 200 mg/L,the pH value was 2.0 and the adsorption time was 2 h,the removal rate of Fe(?)tended to be balanced,and the highest removal rate was 97.84%.The adsorption of Fe(?)by three kinds of modified WCSR conforms to Freundlich isothermal adsorption model and quasi-second-order kinetic model.With the adsorption of Cr(VI)as the index,the modification conditions of nitric acid were optimized.The optimum modification conditions were as follows:the nitric acid concentration was 3 mol/L,modification time was 2.0 h,modification temperature was 30 C,and the optimum ratio of material to liquid is 100g/L.It is concluded that the overall feasibility of converting WCSR into adsorbent by acid/alkali treatment is better.