Compound Modification Of Starch For The Adsorption Of Wastewater Heavy Metals And Its Mechanism

Unlike some organic pollutants which can be degraded biologically,heavy metal ions can not be degraded into harmless final products.Thus,efforts should be done to remove these toxic heavy metals from the wastewater to protect the people and the environment.Starch is a natural polymer which is renewable,low-cost,and biodegradable.In this paper,corn starch and waxy corn starch were used to prepare porous starch.The adsorption of the heavy metal was studied by chemical modification on the porous starch,the adsorption capacity and the adsorption mechanism were studied.In this paper,porous corn starches were prepared by freezing method at different moisture content(75%to 89%)and different freezing temperatures(-20℃ and-80℃),and its structure and adsorption properties were investigated.SEM was used to observe the morphology and pore structure of corn porous starch.FTIR,LCM-Raman and XRD were used to character the short-and long-range molecular orders of the porous starch samples.When the freezing temperature is constant,with the increasing of moisture content from 75 to 89%,the pore size,moisture adsorption,and oil adsorption capacity of porous starch increased greatly,while the apparent density and crystallinity decreased.Under the same moisture content,the apparent densities of porous starch obtained at-20℃ relative to-80℃were small.The crystallinity,pore size,moisture adsorption and oil adsorption were large.The porous starch with excellent specific surface area and large pore structure were obtained by the previous experiments.The porous starch was modified by carbon disulfide to graft the xanthate group,which can effectively chelate the lead ion and adsorb it.Carbon disulfide was successfully grafted to the starch,which was proved by the results of Fourier transform infrared spectroscopy(FTIR),Energy dispersive X-ray spectroscopy(EDX)and Nuclear magnetic resonance(NMR).The adsorption capacity of PSX was highly dependent on the carbon disulfide/starch mole ratio.The results showed that the adsorption process was in good agreement with the Langmuir model.The adsorption kinetic information was studied by pseudo-second-order model and intra-particle diffusion model.The maximum adsorption capacity was 79.2 mg/g for PSX2.15 and the adsorption times was just 20 min.The adsorption mechanism on lead ions of PSX 2.15 was mainly attributed to the chelation effect.The adsorbent has many advantages,such as simply-preparation,rapid adsorption,block form,insoluble in water and easily separated from solution.Compared with the new adsorbents in recent years,PSX2.15 is expected to be a promising adsorbent for the removal of heavy metals.