**Abstract**

A nanomagnetic absorbent based on calcium alginate was produced successfully with the maghemite nanoparticles synthesized in situ, i.e., together with the polysaccharide crosslinking reaction. Physicochemical properties of the absorbent were analyzed and its ability to remove Ni(II) and Mn(II) ions from a real metallurgical industry wastewater was evaluated. Kinetic studies of the adsorption of these heavy metals were realized. To ascertain the most suitable quantity of absorbent to remove Ni(II) and Mn(II) from the wastewater, the absorbent mass was varied and adsorption kinetics was also evaluated. The competitiveness between the metals was evaluated to understand the adsorption mechanism. The samples were characterized by transmission electron microscopy, vibrating sample magnetometry, X-ray diffractometry and Mössbauer spectroscopy. The absorbent prepared, in this work, can be classified as a hydrogel. It presented predominant spherical morphology and micrometric dimension, containing atoms of iron and calcium dispersed uniformly in their internal and external surfaces. The synthesized maghemite nanoparticles presented superparamagnetic behavior. Results showed that the adsorption equilibrium time for both ions was about 60 min. The removal percentages from wastewater were 60.5% for nickel and 56.6% for manganese, using 300 mg of hydrogel. Results revealed that the adsorption mechanism is by ionic change between calcium and heavy metals.

**Keywords:** Nanomagnetic absorbent, hydrogel, calcium alginate, gamma-maghemite, adsorption mechanism, metallurgical wastewater
