Removal of Cr (VI) in Solution Using Agroindustrial Residues of Yam (Dioscorea rotundata)

The present investigation introduces the application of residues of yam-starch process for adsorption of Cr (VI) from aqueous solutions. Numerous methods have been developed to remove heavy metals from wastewater, including physicochemical methods as adsorption. This is not expensive and it is easy to adapt in removal of heavy metals at concentrations below 10 mg/L. The adsorption capacity of residual yam-starch cake at different operating conditions, like the amount of adsorbent and temperature was studied. Batch adsorption experiments were conducted by adding the amount of adsorbent to 100 mg/L sample solutions of Cr (VI). The pH was adjusted to 4 using 0.1 N NaOH and 0.1 N HCl. The 10 mL solution in a 100 mL conical flask was then agitated at 200 rpm in an orbital shaker. The samples were collected after 24 hours and the residual concentration of Cr (VI) was analyzed using Atomic absorption spectroscopy (AAS). The data obtained from the experimental study was subjected to ANOVA to evaluate the effects of different operating conditions on adsorption with all means and standard deviations expressed in duplicates. The results showed percentages of removal higher than 90% achieved at all operating conditions studied and maximum experimental adsorption capacity obtained over 30 mg/g at 55°C and 0.003 g of adsorbent. Binding of heavy metal on residual cake surface was proved by Fourier Transform Infrared Spectroscopy (FT-IR) finding that after heavy metal adsorption, the functional groups OH, C=O, OH y C-O-C changed. This study demonstrated that this material has a high ability for adsorption of Cr (VI) ions from aqueous solution.