Optimization and Modeling of Cyanide Removal from Cassava Waste Water Using Calcined and Activated Adsorbent Mixtures of Oyster Shell and Periwinkle Shell Ash

Abstract

Cyanide, a toxic compound found in cassava wastewater which on frequent basis is discharged to the environment poses danger to the ecosystem; this research work aims to curb this menace. Temperature, pH, dosage, contact time, adsorbent mixture ratio and initial concentration were optimized using CCD on periwinkle-oyster shells composite mixtures for activated and also, calcined adsorbents on the cyanide adsorption from cassava wastewater. Three RSM models (linear, 2FI and quadratic) were applied to study, optimize and predict this adsorption process. ANOVA showed that quadratic model best predicted the processes for both the activated and calcined adsorbents having R2 values of 0.9678, CV% of 15.51% for the activated and R2 values of 0.9550, CV% of 18.54% for the calcined composite adsorbent. Surface and contour plots were generated to study the interaction between the adsorption parameters and cyanide adsorption. Results from this study also show that pH and initial cyanide concentration were the most determining factors of the adsorption process for both adsorbent samples with the highest adsorption capacity of 96.648% and 96.112% obtained for the activated and calcined composite adsorbent respectively. Numerical optimization was carried out and the confirmation test on the analyzed best-fit quadratic models yielded actual adsorption efficiency of 90.174% as against the predicted adsorption efficiency of 89.83% for the activated and actual adsorption efficiency of 82.274% as against the predicted adsorption efficiency of 83.475% for the calcined composite adsorbent hence, confirms that both activated and calcined adsorbents of oyster-periwinkle shells composite mixture is effective for cyanide adsorption from cassava wastewater and the RSM models were effective to optimize and predict the process.