Search for a command to run...
The so rbent power of hydrotalci te compound [Mg3AI (OH)g hCO)XH20 for Cr(VI ) fr om water solution has been evalu ated. The adsorption behaviour of Cr(VI) was investigated at different initial concentration of adsorbate, co ntact time, pH, temperature and adsorbent dose by batch equilibrium technique. The extent of adsorpti on decreased from 23 .2 mg to 4.9 mg with in crease in pH from 2.0 to 10.0. The adsorption of Cr(VI) proceeds predominantly by the ani on-exchange mechanis m. A reacti on kinetic study was undertaken by considering adsorption of the Cr(VI ) o n the outer surface as well as diffu si on within th e pores of th e adsorbent. The mass-transfer coefficients as a fun ction o f temperature were calcul ated to ex pl ain th e results. The adsorption fo llo ws first-order kineti cs . A Langmuir isotherm model fit s th e equilibrium data well. Thermodynamic parameters such as !:lG I , Mil and !:lSI were calcul ated to predict the nature of adso rpt ion. Desorpti on stu dies showed th at about 95.7% of Cr(VI) can be desorbed from the adsorbent at 0.1 M NaOH. The effi ciency of th e adsorbent to remove Cr(VI ) from synthetic wastewater has also been tested . Chromjum has varying valencies, but among these trival ent and hexavalent states are common. When low level s are prese nt in the environment, trivalent chromium apparently plays an essential role in plant and anima l metabolism, while hexavalent chrorruum is directl y toxic to man, animals and plants l . Elevated environme ntal level of chrorruum comes from a variet y of sources. The pote ntial sources of chrorruum include leath er tanning, paints, dyes, mmmg, photographical materi als, steel and alloys and cement industri es 2 The max imum level perrrutted to hexava lent chromium in wastewater is O.OS mg/L. Various methods e xis t for the removal of hexavalent chromium from aqueous solutions, viz. , chemical reduction and precipitation , adsorpti on and ion exchange' . Adsorpti on is by far the most versatile and widely used process . Adsorpti on of Cr(VI) on activated carbon and -other adsorbents have bee n the subject o f va ri ous studi es over recent years4. There a re many o ther insolu ble materi als other than activ ated ca rbon. that have th e pote nti al fo r removi ng heavy metals fro m waste wate rs such as natural and synthet ic zeo lit es. c lays and modified clay mjnerals, al umina a nd resi ns 5 6 . In recent years, greater att ention has bee n g i ven to the stud y of hydrota lci te clays and th eir us e in c hromatogra phy and catalytic refining7. Hyci rotalci ll' ( HT) compounds of empirical formul a [(M~~xM;+(OH)JrX~~m H20 , have positively charged brucite layers neutralised with interlayer anions, and water molecules occupying interlayer .