Nickel(II) carbonate
Nickel(II) carbonate describes one or a mixture of inorganic compounds containing nickel and carbonate. From the industrial perspective, the most important nickel carbonate is basic nickel carbonate with the formula NiCO(OH)(HO). Simpler carbonates, ones more likely encountered in the laboratory, are NiCO and its hexahydrate. All are paramagnetic green solids containing Ni cations. The basic carbonate is an intermediate in the hydrometallurgical purification of nickel from its ores and is used in electroplating of nickel. Structure and reactions. NiCO adopts a structure like calcite, consisting of nickel in an octahedral coordination geometry. Nickel carbonates are hydrolyzed upon contact  with aqueous acids to give solutions containing the ion [Ni(HO)], liberating water and carbon dioxide in the process. Calcining (heating to drive off CO and water) of these carbonates gives nickel oxide: The nature of the resulting oxide depends on the nature of the precursor. The oxide obtained from the basic carbonate is often most useful for catalysis. Basic nickel carbonate can be made by treating solutions of nickel sulfate with sodium carbonate: The hydrated carbonate has been prepared by electrolytic oxidation of nickel in the presence of carbon dioxide: Uses. Nickel carbonates are used in some ceramic applications and  as precursors to catalysts. Natural occurrence. The natural nickel carbonate is known as gaspéite - a rare mineral. Basic Ni carbonates also have some natural representatives. Safety. It is moderately toxic and causes low irritation. Avoid prolonged contact.