Highly-efficient treated oil shale ash adsorbent for toxic dyes removal: Kinetics, isotherms, regeneration, cost analysis and optimization by experimental design

Abstract The environment and human health protection as well as the search for promising and cost-effective materials to eliminate hazardous dyes are a main contemporary worldwide challenge. In this regard, improving the morphology and the specific surface area of the oil shale ash leading to highly efficient innovative adsorbent for the removal of Crystal Violet (CV) and Methyl orange (MeO) dyes. In this research work, we prepared and characterized the treated oil shale ash (TOSA) adsorbent through XRD, XRF, FTIR, pHpzc, SEM-EDX, TEM, and BET. The chosen material’s selectivity and sensitivity depend on the pH and the foreign ions' strength due to the competition between different charges present in the colored solution. The adsorption capacities of CV and MeO, under conditions of dye concentration 100 mg L−1 with adsorbent dose 0.5 g L−1, are 168.88 mg g−1 and 72.26 mg g−1 respectively. Furthermore, a monolayer pattern could be assigned to the Langmuir adsorption model and the equilibrium kinetics of adsorption is best approved by the pseudo-second-order model for the two dyes. According to response surface methodology, the experimental values for CV and MeO were consistent with the predicted values that lead to the maximum dye removal rate of 99.98% and 67.13% respectively. The regeneration results confirm the performance of our adsorbent after several adsorption-desorption cycles. The capital cost of the treated materials used for adsorption was estimated to be around $ 2.15 for 1 g which means that is a non-expensive process for the future valorization of natural resources.