title: The adsorption of chromium (VI) from industrial wastewater by acid and base-activated lignocellulosic residues.
abstract: This study deals with the adsorption of Cr(VI) from synthetic and industrial wastewater, produced by a sewage plant. The activated carbons were prepared from a lignocellulosic raw material by thermal treatment at 450 and 650 degrees C in the presence of acid (AlCl(3), HCl, H(3)PO(4) and H(2)SO(4)) and base (NaOH) agents. To optimize the adsorption of Cr(VI), the chemical modifications caused by each activating agent (related to the capability of Cr(VI) removal), and the optimal experimental conditions of the pH, Cr(VI) concentration, adsorbent dose and residence time, were studied. Thus, treatment with H(3)PO(4) gives rise to carbons with a high surface area and high efficiency for Cr(VI) removal at short equilibrium times. In contrast, the generation of active surface sites by means of NaOH requires longer equilibrium times, the adsorption being less effective than in the former case. The adsorption isotherms obey the Langmuir equation only in the first stages of the reaction but fit the Freundlich equations over the whole range studied, so the heat of adsorption can be easily calculated. The results also show that the activated carbons obtained can be recovered by filtration with an efficiency of 30% in the third cycle.
authors.affiliation: Instituto Nacional del Carbón, CSIC, Department of Chemistry of Materials, PO Box 73, 33080 Oviedo, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Alvarez
authors.forename: Clara
authors.initials: C
authors.lastname: Blanco
authors.forename: Marcos
authors.initials: M
authors.lastname: Granda
mesh_terms: D000327:Adsorption; D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000737:chemistry; D002244:Carbon / Q000737:chemistry; D002482:Cellulose / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D002857:Chromium / Q000737:chemistry*; D003247:Conservation of Natural Resources; D006851:Hydrochloric Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D008031:Lignin / Q000737:chemistry*; D010316:Particle Size; D010756:Phosphoric Acids / Q000737:chemistry; D012972:Sodium Hydroxide / Q000737:chemistry; D013464:Sulfuric Acids / Q000737:chemistry; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D017607:Aluminum Compounds; D002712:Chlorides; D007220:Industrial Waste; D010756:Phosphoric Acids; D013464:Sulfuric Acids; D014874:Water Pollutants, Chemical; D002857:Chromium; C036909:lignocellulose; C074702:chromium hexavalent ion; D000077410:Aluminum Chloride; D012972:Sodium Hydroxide; D002244:Carbon; D002482:Cellulose; D008031:Lignin; C030242:phosphoric acid; C033158:sulfuric acid; D006851:Hydrochloric Acid