*Article* **Removal of Cobalt (II) from Waters Contaminated by the Biomass of** *Eichhornia crassipes*

**Ismael Acosta-Rodríguez <sup>1</sup> , Adriana Rodríguez-Pérez <sup>2</sup> , Nancy Cecilia Pacheco-Castillo <sup>1</sup> , Erika Enríquez-Domínguez <sup>1</sup> , Juan Fernando Cárdenas-González 2,\* and Víctor-Manuel Martínez-Juárez <sup>3</sup>**


**Abstract:** Due to the increase in contamination of aquatic niches by different heavy metals, different technologies have been studied to eliminate these pollutants from contaminated aquatic sources. So the objective of this work was to determine the removal of cobalt (II) in aqueous solution by the biomass of the aquatic lily or water hyacinth (*Eichhornia crassipes*) which, is one of the main weeds present in fresh water, due to its rapid reproduction, growth, and high competitiveness, by the colorimetric method of the methyl isobutyl ketone. The removal was evaluated at different pHs (4.0–8.0) for 28 h. The effect of temperature in the range from 20 ◦C to 50 ◦C and the removal at different initial concentrations of cobalt (II) of 100 to 500 mg/L was also studied. The highest bioadsorption (100 mg/L) was at 28 h, at pH 5.0 and 28 ◦C, with a removal capacity of 73.1%, which is like some reports in the literature. Regarding the temperature, the highest removal was at 50 ◦C, at 28 h, with a removal of 89%. At the metal and biomass concentrations analyzed, its removal was 82% with 400–500 mg/L, and 100% with 5 g of natural biomass at 20 h. In addition, this completely removes the metal in situ (100 mg/L in contaminated water, at 7 days of incubation, with 10 g of natural biomass in 100 mL). So, the natural biomass can be used to remove it from industrial wastewater, even if in vivo, only eliminate 17.3% in 4 weeks.

**Keywords:** contaminants; heavy metals; removal; cobalt; water hyacinth; biomass
