Abstract

Introduction: Contamination of water by toxic heavy metals through the discharge of industrial wastewater is a worldwide environmental problem. Up to now various methods of removing of heavy metals from aqueous solutions have been considered, including use of agricultural wastes as a low cost adsorbent.

Objective: The purpose of this study was to compare nickel removal from aqueous solutions by natural rice straw and modified with citric acid.

Materials and Methods: This study was non-continuous experiment carried out under laboratory conditions by changing effective factors such as pH(2 to 7), contact time(5 to 180 minutes), nickel concentration(1 to 80 ppm) and natural and modified rice straw dosage(0.9 to 5 g/l). The concentration of nickel was measured by atomic adsorbtion in accordance with standard method. Data was analyzed using ANOVA test.

Results: Optimum pH and equilibrium time by the two adsorbents were 5 and 90 minute, respectively. The efficiency of adsorbtion rate increased with increase of the initial concentration of nickel and the increase of adsorbent dose. Efficiency of natural and modified rice straw in the optimum state was 55% and 80% respectively. The kinetic and isotherm was pseudo second order and Langmuir, respectively.

Conclusion: According to the results, rice straw appears to be suitable, low cost and efficient adsorbent for removing ni(II) from aqueous solutions.