Nickel(II) selenate

Nickel(II) selenate is a selenate of nickel with the chemical formula NiSeO4.

Preparation
Nickel(II) selenate can be produced by the reaction of nickel(II) carbonate and selenic acid.


 * $$\mathrm{ NiCO_3 \ + H_2SeO_4 \rightarrow NiSeO_4 + H_2O + CO_2 \uparrow}$$

Properties
Nickel(II) selenate hexahydrate is a green solid. It is tetragonal, space group P41212 (No. 92). At 100 °C, nickel(II) selenate hexahydrate slowly loses water to the tetrahydrate, with space group P21/n (No. 14). At 510 °C, nickel(II) selenate decomposes directly into nickel selenite, which on further heating decomposes into nickel oxide and selenium dioxide.


 * $$\mathrm{ NiSeO_4\cdot 6H_2O \ \xrightarrow[-H_2O]{100\,^\circ C}\ NiSeO_4\cdot 4H_2O \ \xrightarrow[-H_2O]{300\,^\circ C}\ NiSeO_4\cdot H_2O \ \xrightarrow[-H_2O]{390\,^\circ C}\ NiSeO_4 \ \xrightarrow[-O_2]{510\,^\circ C}\ NiSeO_3 \ \xrightarrow[-SeO_2]{690\,^\circ C}\ NiO }$$

It and potassium selenate are cooled and crystallized in hot aqueous solution to obtain the blue-green [Ni(H2O)6](SeO4)2.


 * $$\mathrm{ K_2SeO_4 \ + NiSeO_4 + 6H_2O \rightarrow K_2[Ni(H_2O)_6](SeO_4)_2 }$$