Ni-smectitic ore behaviour during the Caron process

Abstract

Niquelândia is a nickel-lateritic ore deposit located in the State of Goiás, Brazil. This deposit is one of the best-known nickel-lateritic orebodies in Brazil and contains both oxidized and silicate ores. In the oxidized ores, nickel is essentially associated with goethite, while in the silicate ores, it is associated with clay minerals, especially smectites. Two types of smectites were found: a nickel-magnesium-rich trioctahedral and an aluminium‑iron-rich dioctahedral structure.Nickel was produced at Niquelândia by the Caron process, a reduction roasting operation followed by ammoniacal leaching; however, due to the collapse of the nickel prices, Niquelândia mine interrupted its activities in 2016. Usually, the Caron process is able to extracts over 90% of Ni from the oxidized ore and less than 60-70% from the silicate ore. At Niquelândia the nickel recoveries varied from 70 to 75% of nickel from the Run of Mine (oxidized+silicate ores).A detailed study of the mineralogy from the silicate ore residues of the Caron process was conducted in order to find out why nickel extraction is not properly performed in this type of ore. The results revealed: 1) higher nickel extraction is assigned to iron-rich dioctahedral smectites and 2) lower nickel extraction is assigned to nickel-rich trioctahedral smectites; finally, 3) the low Fe content of Ni-rich trioctahedral smectites does not allow forming Ni-Fe phases which can be dissolved by the ammoniacal leaching.