Study On Heavy Metal Adsorption In Biological Adsorbent By Calcined Shrimp Shells

With the advance of industrialization,heavy metal pollution in water is becoming more and more serious,which leads to the accumulation of heavy metals in food,which ultimately endangers human health.Traditional methods of removing heavy metals from water are limited in many areas.The biomass adsorption materials gradually attract the attention of people.As a cheap and readily available solid waste,shrimp shells can be used as a raw material for removing heavy metals from water.In this paper,the adsorption materials are prepared by using a simple and less polluted pyrolysis method.Under the protection of N₂,the pyrolysis was performed under 600?,700?,800?,900?and 1000?,and the shrimp shell basic biological adsorbent was obtained.After cracking,the adsorbent were activated by KOH and Zn Cl₂ respectively in800?and microwave conditions.The samples were characterized by field emission scanning electron microscopy?FE-SEM?,automatic surface area and pore size analyzer,X-ray single crystal diffraction?XRD?and infrared spectrometer?IR?.Then the adsorption characteristics of shrimp shell biomass carbon for Cr⁶⁺and Cd²⁺were analyzed.At the same time,the adsorption mechanism of the adsorption process were studied by Langmuir,Freundlich isothermal adsorption models,first-order,second-order kinetic models,and intraparticle diffusion models.At last,the adsorption of Cr⁶⁺and Cd²⁺on shrimp shell-based biosorbent under multicomponent system was also studied.The main results are as follows:?1?The specific surface area of the abandoned shrimp shell was 3.782 m²/g.Nitrogen protection under the 600-1000?under constant temperature cracking 3h,the BET specific surface area of the highest at 800?under the cracking of shrimp shell,36.644 m²/g.The specific surface area of the adsorbent after KOH activation was 3159.648m²/g,and the surface area was 1668.866 m²/g after the microwave activation of ZnCl₂,and the activation effect of the two methods was significant.The adsorption and desorption isotherms can be obtained before and after activation,which greatly increases the performance of adsorbent.?2?More pore structures and surface microcrystals were formed on the surface of the abandoned shrimp shells after pyrolysis and activation.The microcrystalline?002?of the graphite structure was found in the adsorbent by XRD.After activated,the adsorbent has oxygen-containing functional groups such as CO₃^2-and-OH groups on the surface,and the activation does not change the surface chemical properties.?3?The effects of initial pH value,amount of adsorbent,adsorption time,and initial concentration of heavy metal ions on the removal of Cr⁶⁺and Cd²⁺from wastewater by the biosorbent were studied.The results showed that the activated shrimp shell biomass adsorbent was most suitable for removal of Cr⁶⁺under acidic conditions.The optimum amount of adsorbent was 0.25 g.The adsorption reaction basically reached equilibrium within 80 min,and the initial metal solution concentration was less than 100 mg/L,the adsorption effect is better.The removal of Cd²⁺by the shrimp shell-based biosorbent is most suitable under alkaline conditions.After the amount of adsorbent used is 0.2g,the adsorption amount increases slowly.The adsorption reaction basically reached equilibrium within 80min,and the adsorption effect was Cr⁶⁺>Cd²⁺,and the adsorption capacity of KOH after high temperature activation was higher than that of ZnCl₂ after microwave activation.?4?After adsorption,the biosorption of Cr⁶⁺and Cd²⁺by the biosorbent met the Langmuir and Freundlich adsorption isotherm models.But,the adsorption of heavy metals by KOH adsorbent at high temperature is closer to the Langmuir model,and the activation of ZnCl₂ is closer to the Freundlich model.?5?The adsorption processes of activated adsorbents for Cr⁶⁺and Cd²⁺all conformed to the first-order and second-order kinetic models and the intraparticle diffusion model,indicating that the adsorption process has an influence on the adsorption.?6?In the mixed heavy metal solution,the interference ion Cu²⁺played an inhibitory role in the adsorption of Cr⁶⁺,but had no significant effect on Cd²⁺.