Background: Azo dyes have many applications in various industries. In addition to Mutagenic and carcinogenic potential to humans, these materials cause the production of toxic byproducts in the aqueous solutions. In this study, magnetite nanoparticles were synthesized with modified sodium alginate. Then their efficiencies in absorbing Acid Red 18 dye were investigated.

Methods: First, magnetite nanoparticles were synthesized by chemical co-precipitation method and then modified magnetite nanoparticles were evaluated as an adsorbent for Acid Red 18 dye adsorption. TGA test was used for proving modified magnetite nanoparticles coating.

The effects of pH, contact time, nanoparticles and Acid Red 18 dye concentrations were studied.

Residual concentration of Acid Red 18 dye was read using a spectrophotometer at a wavelength of 508 nm. Data was explained by the Langmuir isotherm and Freundlich models.

Results: In optimal conditions of operation including pH = 5, contact time =30 minutes, adsorbent dose 0/2gr/l and the initial concentration of Acid Red 18 dye= 50 mg/l, removal efficiency of the process was obtained over 95 %. These studies also showed that Acid Red 18 absorption pattern has more conformity with the Freundlich model.

Conclusion: The results showed that sodium alginate is a convenient and inexpensive coating for magnetite nanoparticles; also it has high efficiency to absorb dye Acid Red 18 in a short time.