removal of acid orang 7(ao7) dye from aqueous solution by using of adsorption on to rice stem waste: kinetic and equilibrium study

background and purpose: dye is widely used in industries such as cosmetic, leather, paper and textile and release to the environment via their effluents. the purpose of this study was to compare the efficiency of low-cost adsorbents in acid orang 7 dyes removal from water. materials and methods: the rice stem biomass was sun dried, crushed and sieved to particle sizes in range of 1-2 mm. then treated with 2.0 mol/l nitric acid for a period of 1 h followed by washing with distilled water and finally washed stem was dried at 105◦ in oven. the residues concentration of acid orang 7 dyes was measured by spectrophotometer in λmax of 452 nm. the effect of ph, contact time and initial ao7 dye concentration, kinetic and isotherm models were studied. then data interpreted and analyzed by excel 16 software. results: the ph value of 3, contact time of 75 min, adsorbent dosage of 8 g/l and dye concentration were 10 mg/l determined as optimum conditions for adsorbents. the most acid orang 7 dyes removal efficiency of 98% was obtained for modified rice stem in optimum conditions. the equilibrium data is best fitted on langmuir isotherm and the adsorption kinetic model follows pseudo-second model. conclusion: based on data obtained in this study, it can be concluded that adsorption by modified rice stem