Terra Rossa Soil as an Adsorbent to Remove Hexavalent Chromium in Aqueous Solutions

Abstract

Kaolinite is a phyllosilicate clay of type 1:1 which is usually associated with iron oxides in nature. The clay is abundant in Terra Rossa soils which is located in the Gunungkidul, karst area. Based on the structure and nature of it’s the charge, it has the potential to adsorb anionic heavy metals, especially hexavalent chromium. Heavy metal chromium in the form of hexavalent is very dangerous for human health and the metal is mostly produced from the waste of leather tanning factories that are widely available in Yogyakarta. The purpose of this study was to investigate the possibility of using Terra Rossa soil as an adsorbent to remove heavy metal Cr (VI) from aqueous solution. The experiment was carried out by mixing the adsorbent with a dose of: 1 – 4.5 grams of fine soil, Φ 0.5 mm into a 50 ml solution containing 10 ppm chromium with pH 5 and 3. Stirred at 200 rpm for 2 hours, then centrifuged 3500 rpm for 20 minutes. The filtrate was given phosphoric acid and diphenyl carbazide and then measured using a spectrophotometer with a wavelength of 540 nm. The results showed that the average percentage of chromium removal at pH 5 = 30%, while pH 3 = 49%. The adsorbent absorption (mg/g) decreased in line with increasing adsorbent dose. Absorption graphs of Freundlich and Langmuir models in pH3 solution show R2=0.9264 and 0.9361 respectively, while in pH5 solution the R2 values are 0.3752 and 0.3461, respectively. Adsorption capacity according to Freundlich = 1.7331 mg/g, while according to Langmuir = 5.28 mg/g with adsorption site affinity 0.1894 L/mol.