Cow bone charcoal (CBC) was synthesized and used for the removal of metals ions (manganese, iron, nickel and copper) from aqueous solutions. Two different adsorption models were used for analyzing the data. Adsorption capacities were determined: copper ions exhibit the greatest adsorption on cow bone charcoal because of their size and pH conditions. Adsorption capacity varies as a function of pH. Adsorption isotherms from aqueous solution of heavy metals on CBC were determined. Adsorption isotherms are consistent with Langmuir´s adsorption model. Adsorbent quantity and immersion enthalpy were studied.

Adsorption is a broadly used process for the removal of heavy metals and the world trend is directed to the application of new technologies to intensify existing processes. The properties of the magnetic field (intensity and arrangement) and the intrinsic magnetic properties of the adsorbent and the adsorbate are decisive for satisfactory results. The intensity of the magnetic field is important, because this implies that the greater number of spins present will align with the magnetic field according to the magnetic nature present, allowing the mobility of the adsorbate and generating heterogeneity on the surface of the adsorbent. Similarly, the arrangement of the magnetic field will determine the direction of the magnetic field lines. The application of a magnetic field as an alternative for the intensification of the adsorption process based on the consideration that the magnetic field is safe, environmentally friendly and economic.

The application of static magnetic fields during adsorption as an unconventional method for the removal of heavy metals such as Cd2+ and Zn2+ was studied in this work. Two different materials were employed as adsorbents: activated carbon from bituminous coal and bone char. The magnetic characterization of these materials reveals that the activated carbon from bituminous coal is a ferromagnetic material, while the bone char is a paramagnetic material. Both adsorbents were used as received; i.e., no additional modification was employed to alter or improve their magnetic properties. Adsorption studies included adsorption isotherms at 30 °C, at pH 5, and equilibrium times of 72 h. The adsorption results obtained depended on the magnetic nature of both the adsorbent and the adsorbate. It was determined that because of its ferromagnetism (hence, its chemical composition), the activated carbon performed better when an external magnetic field was present during the adsorption process. An increase of 63% and 15% in its adsorption capacity was measured for Cd2+ and Zn2+, respectively.

Recovery of phosphates from an anodizing industry wastewater was studied by chemical precipitation. Samples of wastewater were selected attending to the highest phosphate concentration observed during 1 year of weekly sampling. Different types of precipitant agents were analyzed in batch systems. Results showed that it is possible to remove 100 % of phosphates when Ca(OH) 2 is used as precipitant agent. The best conditions of precipitation were found following a L 9 orthogonal array design of the Taguchi method. For an initial concentration of phosphates of 4336 mg/L, these best conditions were a Ca/P molar ratio of 5.77, pH 2, stirring time of 15 min and settling time of 1 h. Additionally, it was demonstrated that the factors with more influence in the precipitation of phosphates with Ca(OH) 2 were the pH of the wastewater and the stirring time. When the phosphate removal was performed at pH 6 and 10, hydroxyapatite Ca 5 (PO 4 ) 3 (OH) was found in the

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