Use of activated carbon for the recovery of chromium from industrial wastewaters

Abstract

:A technique for the removal and recycling of hexavalent chromium from electroplating industries was developed. It involves a two-phase process which consists of (1) the use of an activated carbon bed for the accumulation of chromium onto the surface of activated carbon followed by (2) the regeneration of the carbon leading to a concentrated chromium solution with potential for reclamation or reuse within the plating operation. Results from continuous ýow experiments showed that in excess of 99% chromium removal efficiency can be achieved. It was also revealed that regeneration of the exhausted carbon under acidic conditions recovered chromium in the trivalent state with concentrations as high as 3 g dm~3, more than 12 times the inýuent concentration. The adsorption capacity of the activated carbon was found to increase with successive cycles of adsorption/regeneration. However, when regeneration was achieved under alkaline conditions, the chromium was recovered in the hexavalent state with concentrations as high as 8·4 g dm~3, in excess of 33 times the chromium inýu-ent concentration. In addition, under caustic regeneration conditions, the data showed that the adsorption capacity in this case decreases with the increased number of exhaustion cycles. Mass balance calculation for both acid and caustic regeneration indicated that in both cases the regeneration process was incomplete with a recovery efficiency averaging around 50%. In an attempt to maximise the recovery efficiency, a combination of caustic followed by acid regeneration was applied to the exhausted activated carbon and the results led to a drastic improvement in the total recovery process (85-98%). These results clearly show that activated carbon is a viable candidate for the removal and recovery of chromium from electroplating industries. The critical advantage in the use of activated carbon is (1) the ability to regenerate and thus prepare a concentrated chromium solution for potential reclamation or recycle to the plating operation, and (2) the potential of avoiding the generation of hazardous sludge for land disposal.

Adsorption kinetics and intraparticulate diffusivities of Hg, As and Pb ions on unmodified and thiolated coconut fiber

“…Sorption or the removal of toxic or heavy metals from aqueous effluent has been extensively studied in recent times. The use of conventional methods has been reported such as activated carbon or activated alumina (Shim, et al, 2001;Ouki, et al, 1997;Monser and Adhoum, 2002) and so on. Also, the use of the ion exchange resins and precipitation methods has been the most efficient and effective method for removing heavy metals from aqueous effluents, but these are very expensive.…”

Removal of heavy metal from industrial wastewater using chitosan coated oil palm shell charcoal

“…However, it is not economically appealing because of high operational cost. Adsorption using commercial activated carbon (CAC) can remove heavy metals from wastewater, such as Cd (Ramos et al 1997); Ni (Shim et al 2001); Cr (Ouki et al 1997); Cu (Monser and Adhoum, 2002). However, CAC remains an expensive material for heavy metal removal.…”

Equilibrium sorption isotherm studies of Cd(II), Pb(II) and Zn(II) ions detoxification from waste water using unmodified and EDTA-modified maize husk

“…It is non-polluting, and it can be highly selective, more efficient, easy to operate and hence cost effective. Also, adsorption using activated carbon have been reported (Ouki and Neufeld, 1997;Shim et al 2001;Monser and Adhoum, 2002).…”