Utilization of coal fly ash and grape waste to remove toxic metal ions in mining waste waters

Abstract

In recent years, the studies of a variety of inexpensive adsorbents as alternative to the expensive activated carbon have received a lot of attention. The purpose of my research was primarily focused on the modification of Thunder Bay coal fly ash, the characterization of the pristine and modified fly ash and the application of modified fly ash for removal of metal ions from mine wastewater. Adsorption by grape wine material (GWM) was also investigated though not completed. Modification at low and elevated temperatures with 2.0 M NaOH yielded improvement in surface area, pore volume and cation exchange capacity. However, low-temperature modification was pursued leading to very efficient adsorbents named TBRM and TBFZ compared to the original fly ash named TB. The modified and unmodified fly ash was characterized using different techniques including ICP-OES, X-ray diffraction, specific surface analysis (Brunauer-Emmet- Teller), particle size distribution analysis and scanning electron microscopy. Surface area analysis revealed an increase of specific surface area from 1.24 (TB) to 64.34 (TBRM) and 68.98 (TBFZ) m2/g, respectively. Likewise, porosity was also induced in the modified fly ash. Cation exchange capacities were determined as 1.94, 23.48 and 29.23 meq/g for TB, TBRM and TBFZ, respectively. SEM-EDS and XPS were employed to confirm the adsorption of metal cations on the surface of the adsorbents. The performance of TBRM and TBFZ for the removal of Cu2+, Pb2+, Ni2+, Cr3+, Co2+ and Cd2+ from a synthetic cocktail solution (SCS) and tailing pond water (TPW) was compared to that of TB. Results indicated TBRM and TBFZ were more efficient in both SCS and TPW. A batch method was used to study the influential parameters of the adsorption process including contact time, pH effect, and kinetics and adsorption isotherms. Column studies were done to compliment the batch mode approach. Regeneration of TBFZ revealed a possible 3-cycle application. The equilibrium data were generally modeled by the Langmuir and Freundlich models. Also, the pseudo-second order model was found to explain the adsorption kinetics most effectively. Thermodynamic studies of Ni2+ and Cu2+ with TBFZ in SCS revealed that the adsorption process was spontaneous although endothermic with a decrease in entropy. The most efficient adsorbent TBFZ was converted into innovative concrete foam composite material TBFZ:FA:BA 0.22:0.33:0.45, for adsorption studies. Preliminary studies revealed a removal of more than 95 % of Cu2+, Pb2+, Ni2+, Cr3+, Co2+ and Cd2 in both SCS and TPW after 6 h of contact. However, the regeneration of TBFZ:FA:BA 0.22:0.33:0.45 was inefficient and further investigation ought to be carried out. Overall, the results indicate a significant potential of the modified Thunder Bay fly ash as an inexpensive and effective adsorbent for the removal of toxic metals from mine wastewater.