Migration and Aggregation Behavior of Nickel and Iron in Low Grade Laterite Ore with New Additives

This study focused on the preparation of high-grade ferronickel concentrate, the behavior of efficient migration and the polymerization of ferronickel particles during reduction roasting, by adding calcium fluoride and a ferronickel concentrate to low-grade laterite ore from Yunnan. The effects of temperature, holding time, reductant content, ferronickel concentrate content and magnetic field intensity on the preparation of the ferronickel concentrate were studied and the optimum conditions were determined as follows: 30% ferronickel concentrate (metal Ni-4.68%, metal Fe-45.0%), 8% coal, 7% calcium fluoride, reduction temperature of 1250 °C, reduction time of 60 min and the intensity of magnetic separation is 150 mT. The proportion of nickel and iron in ferronickel concentrate was 88.7% (metal Ni-8.62%, metal Fe-80.1%), and the recovery efficiency of nickel and iron are 98.8% and 82.4%, respectively. X-ray diffraction and scanning electron microscopy indicated that ferronickel-concentrate, as an activating agent, improved the aggregation effect of ferronickel particles. The efficient migration and polymerization of ferronickel particles in the ore significantly increased the size of the ferronickel particles with additives, therefore a high-grade ferronickel concentrate was prepared, and the reduction and recovery efficiency of laterite nickel ore was improved.

Investigation of the deposition of calcium fluoride nanoparticles on the chips of CaF2 single crystals

The deposition of calcium fluoride nanoparticles on single crystal chips of calcium fluoride was studied. CaF2 nanoparticles were synthesized by co-precipitation from aqueous nitrate solutions using hydrofluoric acid as a fluorinating agent at a batch system. The prepared samples were examined by atomic force microscopy, scanning electron microscopy, transmission electron microscopy and optical transmission. There is an inhomogeneous coating of the substrate surface with submicron particles of about 100–150 nm in size, which are clusters of nanoparticles of 15-20 nm in size. The initial nanoparticles coherently grow on the surface of the crystal substrate. Heat treatment of the substrate-deposited layer composite at 600 °C leads to the coalescence of submicron particles and the formation of a porous layer of a complex structure.

Scanning tunneling microscopy study of CaF2 on Si(111): Observation of metastable reconstructions

The deposition of calcium fluoride (CaF2) on Si(111) at temperatures above 570 °C has been studied with scanning tunnelling microscopy (STM). At such temperatures, triangular calcium fluoride islands are formed both on terraces and along the phase domain boundaries of the (7x7) reconstruction of the Si(111) substrate. In addition to the formation of islands, we observe that CaF2 molecules react with the substrate inducing larges areas of its surface to reconstruct into (√3x√3) and c(2x4) phases. Upon annealing at 600 °C, the abovementioned areas of (√3x√3) and c(2x4) turn into the stables (3x1) phase due to desorption of fluorine. Calcium fluoride islands are stable at this temperature. Depositions of calcium fluoride performed with Si substrate kept at higher temperatures, namely at 680 °C, lead directly to the formation of the (3x1) phase, without passing though the formation of the metastable (√3x√3) and c(2x4) phases. If CaF2/Si(111) is brought at even higher temperatures, Ca also starts desorbing and the (7x7)-Si(111) reconstruction can eventually be restored.