Physico-Chemical Characterization of Chemically Precipitated Nickel in a Synthetic Aqueous Media

In the liquid-liquid and solid-liquid systems there is possible to promote the chemical precipitation of
certain species by controlling the physical-chemical conditions of the liquid media. In the case of solidliquid
interactions the chemical precipitates can adsorb on the surface of particles modifying their
surface properties (i.e. during milling), whereas for the liquid-liquid system this precipitation
contributes to clean for instance wastewater contaminated with heavy metals.
In this work nickel sulfate hexahydrate (NiSO4 ∙ 6H2O) was dissolved in distilled water, to establish the
physicochemical conditions (pH, electrochemical potential, ionic strength, activity coefficient) that
enhance the chemical precipitation of nickel species.
The chemical analysis of precipitates was carried out by X-ray diffraction, Fourier transformed infrared
spectrometry, and the quantitative chemical analysis of liquids was carried out by atomic absorption
spectroscopy. The zeta potential of nickel precipitates was also determined.
The experimental results show that nickel precipitates as nickel hydroxide (Ni(OH)2) starting
at pH 3, being more evident at pH 9. Nickel precipitates completely at pH 11. From zeta
potential measurements the surface charge goes from negative to positive with the IEP at pH
around 11, such behavior is attributed to the change of nickel hydroxide type from α-Ni(OH)2 to β-
Ni(OH)2.
The functional groups of nickel precipitates were obtained through FTIR spectrometry, where the peak
at 3650 cm-1 represents the free OH group in the β-Ni(OH)2 phase.
From these results, there is possible to propose a cleaning route of water contaminated with
nickel.