Removal of methylene blue dye from water by a spent bleaching earth biosorbent

This work is about the valorization of spent bleaching earth (SBE) at low cost from the AFIA oil refinery in Algeria's western region. The biowaste has been burned to eliminate the oil traces, then it has been valorized in two ways: (i) chemically, using phosphoric acid to obtain SBEC and (ii) thermally at 750 °C to create SBEH. The obtained materials were used for the first time as biosorbents in the wastewater treatment field. The three biomaterials show very interesting adsorption properties, with specific surfaces of 194.2, 784.6 and 888.5 m² g^-1 for SBE, SBEC and SBEH, respectively. The analysis has revealed that the obtained materials are alumino-silicates. The three biowastes have been used to remove methylene blue dye from water. The dye was totally eliminated by a physisorption mechanism in the presence of 1 g L^-1 of each biowaste after 8, 10, 20 min of contact time. The highest correlation coefficient (R² = 0.99) was related to the Langmuir isotherm, indicating a good fit with this model, and explaining the biosorption as a monolayer process. According to this model, the adsorption capacities were 123.3, 185.2 and 188.7 mg g^-1 for SBE, SBEH and SBEC, respectively. This study shows that SBE can be used as an alternative to commercial adsorbents for dye removal from water.