Nickel (Ni) is the third element in Group VIII in the periodic table. It has an atomic number of 28, an atomic weight of 58.69, and a common valence of 2 and less commonly 1, 3, or 4. The average abundance of Ni in the earth’s crust is 1.2 ppm; in soils it is 2.5 ppm; in streams it is 1 μg/L, and in groundwaters it is <0.1 mg/L. Nickel is obtained chiefly from pyrrhotite and garnierite. Nickel is used in alloys, magnets, protective coatings, catalysts, and batteries.
The common aqueous species is Ni2+. In reducing conditions insoluble sulfides can form, while in aerobic conditions nickel complexes with hydroxide, carbonates, and organic ligands can form. It is an essential trace element for plants1 and animals.2 The United Nations Food and Agriculture Organization recommended maximum level for irrigation waters is 200 μg/L. The U.S. EPA primary drinking water standard MCL is 0.1 mg/L.
The atomic absorption spectrometric methods (Sections 3111 B and C), the inductively coupled plasma methods (Sections 3120 and 3125), and the electrothermal atomic absorption spectrometric method (Section 3113 B) are the methods of choice for all samples.