Ni-bearing phyllosilicates ('garnierites'): New insights from thermal analysis, μRaman and IR spectroscopy.

Abstract

Ni-Mg-phyllosilicates, so-called 'garnierites', are significant Ni ores in Ni-laterite deposits worldwide. In addition, they are the natural analogues of synthetic catalysts involving Ni and phyllosilicate substrates used in reactions for the remediation of greenhouse gases. However, the nomenclature, classification and characterisation of Ni-Mg-phyllosilicates is a long-lasting problem, because of their fine-grained nature, poor crystallinity and frequent occurrence as intimate mixtures. This work presents and discusses DTA-TG, Raman and FTIR spectroscopy data of a series of well characterised, naturally occurring Ni-Mg-phyllosilicate samples with a variety of mineral compositions (including serpentine-dominated, talc-dominated and sepiolite-falcondoite, with various Ni contents). The results are compared to data obtained from crystalline, 1:1 and 2:1Mg-phyllosilicates and from the literature. DTA-TG confirmed that the talc-like fraction in garnierite mixtures belongs to the kerolite-pimelite series. The different garnierite types analysed are distinguishable from their Raman and FTIR spectra, and the serpentine, talc and sepiolite components could be identified (e.g. by Raman bands at ~690cm⁠−1, ~670cm⁠−1 and ~200cm⁠−1, respectively). Knowledge of Raman and FTIR vibrations of garnierites with constrained structure and composition is paramount in order to effectively characterise these phyllosilicates, and can be applied to mineral identification in ore exploration and processing, and after synthesis for nanotechnology purposes.