Optimization of an acid digestion for HFSE analyses using ICP-MS: application to the assessment on environmental mobility of HFSE and REE in iron ore tailings

Abstract

A method to optimize an acid digestion procedure for High Field Strength Elements (HFSE) was developed, using mine tailing samples of variable ages (0-10 years old), provided by Iron Ore Company of Canada (IOC). The study included experiments that aimed to find the optimal length of digestion to obtain improved recoveries for HFSE. Different acid mixtures were tested in an attempt to accomplish better digestion of the samples, and to obtain a more stable solution. For the purpose of this research, a stable solution is defined as a solution that would maintain analytes in solution over time. This study concluded that the initial parameters of the acid digestion procedure were the most effective. -- The method development generated large data sets for the elements determined using this procedure. These data were analyzed to assess the environmental mobility of HFSE and REE in the samples. Samples had low concentrations of HFSE and Rare Earth Elements (REE) elements (i.e, Zr 5 ppm, Nb 1.7 ppm, Hf 0.1 ppm, etc). These tailing samples were exposed to weathering since their generation and stored in a dump, located in Labrador. The mobility investigation consisted of exhaustive comparisons of sample elemental concentrations plotted according to their ages. Unexpected variations, suggested the use of different ores or gain/loss of mass that would concentrate/dilute these elements. To understand these variations, sample concentrations were normalized, displaying parallel trends similar to igneous or sedimentary rocks. From these observations, it was concluded that HFSE or REE were not selectively affected during weathering and ores with common HFSE and REE characteristics were used.