Evaluation of Usual and Acid-Modified Fig Leaves Powder Application as a Biosorbent for Removing Chromium (VI) from Aqueous Solutions

Introduction: One of the worrying and increasing environmental problems is urban and industrial waste water pollution, such as chromium (Cr). Given the destructive effects of Cr  and non-degradability, its removal is of great importance. Adsorption method by low-cost biosorbents has been a successful method in during the last decade. This study aims to examine the effect of usual and acid-modified fig leaves powder as a biosorbent for removing of Cr (VI) from a synthetic aqueous solution. Methods: Laboratory tests were designed and implemented, including solution making of Cr (VI) and then  in order to study the effect of different parameters, including solution pH, contact time, solution concentration, and adsorbent dosage, the secondary amount of chromium concentration was measured and compared by atomic absorption spectrometer. Results: The results showed that for usual adsorbent, optimum parameters included pH 2, 200mg/l initial concentration, 40g adsorbent concentration, and 120min equilibrium time while for the modified adsorbent, optimum parameters were pH 3, 300mg/l initial concentration, 40g adsorbent concentration, and 120min equilibrium time. The maximum adsorption percentage of Cr (VI) in the first case was 54.33% and in the second case was 91.50%. In addition, by examining adsorption isotherms and kinetic models, it was found that Cr adsorption in both cases  follows Langmuir isotherm (R2=0.942 for usual and R2=0.975 for modified adsorbent) and pseudo-second order kinetic model (R2=0.976 for usual and R2=0.982 for modified adsorbent). Conclusion: More efficient removal of Cr using a modified adsorbent compared to usual adsorbent and previous studies indicates the suitability of modified fig leaves powder as an adsorbent of Cr (VI).