Research Of Powdered Activated Carbon For The Removal Of Iodide From Brine

Iodine is essential trace elements to human, but excess intake of iodine will beharmful to the body. Some areas with high iodine concentration in water, it will need toreduce the iodine concentration can be edible. The iodine-removing technology has verybig application prospect in food and other industry areas.Membrane cell technology is used in all new chlor-alkali plants. This is due to thefact that the expenditure concerning capital investment, operating costs and energyconsumption, is lower than that of diaphragm and membrane technology. What is more,this is the most environmental friendly technology, yet this technology requires a highpurity brine. One of the most important parameters to be monitored is the concentrationof iodide ion. In the electrolysis cell, iodide is oxidized to iodate, which precipitates inthe ion-exchange membrane and decreases the membrane’s useful lifetime. So thepresence of iodide in brine is the direct reason leading to the damage of ion-exchangemembrane. However, the ion-exchange membrane is quite expensive, the productioncosts will increase greatly if the ion-exchange membrane is changed frequently inchlor-alkali industry. Accordingly, removing iodide from brine is the most effective andeconomical method. In this study, the technique of H₂O₂oxidation coupled withpowdered activated carbon （PAC） to remove iodine from low concentrationiodide-contained chlor-alkali brine was studied. The main contents include thefollowing:①In the process of oxidation of iodide, the optimum condition of iodideconversion was studied, some factors such as different oxidants, the molar ratio ofhydrogen peroxide （H₂O₂） to I-, reaction temperature, pH value and the reaction time oniodide conversion were studied, and the results showed that: in the reaction of H₂O₂, theproducts are water and oxygen, which showed H₂O₂is an suitable oxidant for iodideoxidation, comparing to other oxidants there is no secondary pollution in the reactionsystem.When the molar ratio of hydrogen peroxide （H₂O₂） to I-was1:1, reactiontemperature was40℃, pHwas2, and the reaction time was40min, the conversionefficiency reached to the maximum.②In the process of the adsorption of iodine, the adsorption time, temperature,stirring speed, the amount of powder activated carbon and the influence of coexistenceion were investigated. The results indicated that the optimum conditions for iodine removal were as follows: at a pH range of2⁵the amount of PAC was1.5g/L, theadsorption time was120min, the adsorption efficiency was93.4%and the equilibriumadsorption isotherms can be described by the Freundlich isotherm model, which showedthat PAC can be used as an effective adsorbent for iodine removal from brine andprovides some theoretical basis for the removal of iodide from chlor-alkali brine.③Several different methods to remove iodine ion were in the comparison: in thisexperiment ion resin exchange method, different adsorbent adsorption method, andnanofiltration membrane method to remove iodine in alkali salt water were compared,and the results showed that the adsorption effect of activated carbon was better than thatof ion exchange method, the effect of ion exchange method was better than that ofnanofiltration membrane method. Take the experimental operation process and cost intoconsiderations, powder activated carbon is more appropriate. Further, in this technologycombined the oxidant hydrogen peroxide with powder activated carbon, hydrogenperoxide is pollution-free and will not introduce new impurities, the operation is simple,which provids a possible way for iodine removal and recovery in industrial salt water.④Regeneration of activated carbon: in this experiment activated carbon wasregenerated mainly through chemical method, the effects of elution agent concentration,elution time, temperature and stirring rate and other regenerative conditions wereinvestigated, the experimental results showed that: the powered activated carbon withiodine was eluted in elution agent sodium hydroxide （0.05mol/L）, stirred at the speedof80r/min at30℃for120min can achieve better regeneration elution effect.