Color removal of wastewater from silk dyeing process by using treated fly ash from sugar industry

Abstract

Solid fly ash waste from the sugar industry was treated by HCl and then carbonized under N2 at 900 °C for 1 h. The resulting carbon was used as an adsorbent for the removal of colored dyes from wastewater generated in the silk dyeing process. The untreated fly ash and commercial activated carbon were also used as adsorbents for comparison. Porous properties of all adsorbents were characterized by nitrogen adsorption/desorption at 77 K. The kinetics and equilibrium data were obtained from batch experiments with varying adsorption times (1–12 h) and initial concentrations (50–1,000 mg/L) of conventional commercial dye in wastewater, Dark Red 34. The adsorption isotherms and kinetics were studied for all three samples. The adsorption kinetics were analyzed using pseudo-first order, pseudo-second order and intra-particles diffusion models. The adsorption equilibrium data was analyzed by using Langmuir and Freundlich models. Results showed that the surface area of the treated fly ash increased from 26 to 239 m2/g after acid and carbonization treatments. Equilibrium adsorption was reached in 4 h for all samples. The experimental data indicated that the adsorption kinetics were well described by the pseudo-second order model. While isotherms fitted well with the Langmuir equation. The maximum adsorption capacities for the dye removal were 1258, 1156 and 666 mg/g for treated fly ash, activated carbon and untreated fly ash, respectively. Therefore, treated fly ash from the sugar industry shows its high potential as an adsorbent for the color removal of wastewater from silk dyeing process.