Amorphous adsorbent from geothermal solid waste for methylene blue removal

Abstract

Organic compounds such as dyes and heavy metal ions are common pollutants in waste water that have become a global problem. Adsorption has proven to be a successful technique in removing organic species such as methylene blue (MB). Geothermal solid waste has the potential to be used as an adsorbent due to its silica content. The silica compound in geothermal waste has the potential to be developed as porous material. Aluminium hydroxide and geothermal solid waste were added to the aqueous alkali (sodium hydroxide (NaOH)) in a continuous stirred-tank reactor, which resulted in an amorphous mesoporous material of the natrolite phase. The performance of the geoadsorbent was evaluated through the removal of various concentrations of MB, and isotherm adsorption models were used to evaluate the data. The adsorption mechanisms of MB removal by the geoadsorbent as shown by Fourier transform infrared spectra are electrostatic attraction and hydrogen-bond formation. The geoadsorbent can remove MB up to 84.449%, in which the adsorption is highly dependent on the initial concentration of MB. The Langmuir isotherm model provides the most accurate representation of MB adsorption as a result of the physical process, with a correlation coefficient of 0.971.