Study On The Preparation Of Acid Modified Activated Carbon And Its Removal Of Cr(Ⅵ)

In this paper, activated carbon were modified by acids(include sulfuric acid,phosphoric acid and nitric acid)and the removal of Cr(VI) in aqueous solution bymodified activated carbon was studied. The study identified the best preparationconditions of acid modified activated carbon and the best adsorption conditions ofCr(VI) by selecting Cr(VI) removal rate as index. The adsorption mechanism of acidmodified activated carbon was also preliminarily discussed.The influencing factors of preparing acid modified activated carbon includedacid concentration, modification time and temperature. The experimental resultsshowed that the preparation conditions of sulfuric acid modified activated carbonwere the best when sulfuric acid concentration was1mol/L, modification time was4hand the temperature was60℃; best for phosphoric acid modified activated carbonwhen phosphoric acid concentration was2mol/L, modification time was8h and thetemperature was25℃; best for nitric acid modified activated carbon when nitric acidconcentration was4mol/L, modification time was6h and the temperature was60℃.Compared with the original carbon, the Cr(VI) removal rates of three kinds of acidmodified activated carbon were significantly increased by30%.The factors(include the pH of Cr(VI) solution, initial concentration of Cr(VI)solution, activated carbon dosage and adsorption time)of absorbing Cr(VI) bymodified activated carbon were discussed. The experimental results showed that theadsorption conditions of sulfuric acid modified activated carbon were the best whenthe pH of Cr(VI) solution was3, initial concentration of Cr(VI) solution was50mg/L,activated carbon dosage was0.4g and adsorption time was24h, under this conditionthe removal rate of Cr(VI) was95.79%. The adsorption conditions of phosphoric acidmodified activated carbon were the best when the pH of Cr(VI) solution was3, initialconcentration of Cr(VI) solution was50mg/L, activated carbon dosage was0.5g andadsorption time was24h, under this condition the removal rate of Cr(VI) was97.5%.The adsorption conditions of nitric acid modified activated carbon were the best whenthe pH of Cr(VI) solution was3, initial concentration of Cr(VI) solution was60mg/L,activated carbon dosage was0.5g and adsorption time was24h, under this conditionthe removal rate of Cr(VI) was99.2%.The adsorption of three kinds of acid modified carbon on Cr(VI) at three temperatures(293K,303K,313K)was more in line with the quasi secondary dynamicsequation and the Langmuir isotherm equation, the correlation coefficient R2of whichwere greater than0.99. By SEM, ZPC analysis and Boehm titration experiment on thecharacterization of original carbon and three kinds of acid modified carbon we’ve gotthe following results: the acid modified carbon surfaces became rough with greatlyincreasing number of holes, many shallow holes greatly stretched towards the inside,the surface area was been increased; the pHpzc of acid modified carbon was acidicand its acidity was lower than the original carbon; the content of acidic groups on themodified carbon surface increased compared to the original carbon, therefore thepolarity and hydrophily of modified carbon surface enhanced. The adsorption capacityof modified carbon for heavy metal ions, such as Cr2O72-, was enhanced. And Cr6+candirectly have complexation with oxygenous acidic functional group on the acidmodified carbon surface. All of the above were conducive to the the adsorption ofCr(VI).Three kinds of acid modified carbon functioned better in adsorbing and removingCr (VI) in the wastewater than the original carbon. And their modification methodswere simple, therefore the acid modified carbon had broad application prospects.