Effect of Temperature, pH, and Salinity on Adsorption of Textile Dye onto Biosilica

Abstract

This research presents the adsorption of Direct Red-31 dye with biosilica adsorbent from rice husk ash. Direct Red-31 dye is azo dye, which is frequently used in textile industry. Rice husk ash is used as asdorbent, because of the abundant existence of rice husk in Indonesia and it is easy to get. This research was run in batch process with dye concentration 20 ppm and adsorbent mass 10 g/L. The research was performed with pH variation (2, 3, 4, 5,  and 6), variation of salt (NaCl, NaNO₃, and Na₂SO₄) and temperature variation (35, 40, 45, 50, and 55 ^oC). From the research result, the optimum pH of the adsorption is at pH 2 with percent removal 83.949%. Adsorption process with addition of Na₂SO₄ salt increases the removal percentage to 87.714%. For the temperature effect analysis, the positive value of ΔG indicates the non spontaneous adsorption, the entalphy (ΔH) value of 11.8 kJ/mol indicates the adsorption was physical and endothermic. Entropy (ΔS) value of 0.03101 kJ/mol indicates structural changes on the surface of the adsorbent.