Chemical analysis of ores

X-ray fluorescence chemical analysis quantifies the elemental composition of solid and liquid samples. 

Typical Use:

• • – Rapid analysis for major and trace elements (mass percent) and trace (ppm) (1ppm = 1 mg/kg = 1 gram/ton = 0.0001 mass %)
  • – Detection of elements ranging from Be to Uranium
  • – Widely used for total rock analysis in geology

The technique involves bombarding the sample with X-rays, which causes its atoms to become excited and, when they return to their ground state, re-emit energy in the form of X-rays with energy and wavelength characteristic of each element present; this is X-ray fluorescence, or secondary X-ray emission. The X-rays emitted by the sample are then measured to quantify the mass concentrations of elements present.

There are two systems of X-ray fluorescence depending on how the X-rays are detected :

• – a wavelength dispersive X-ray fluorescence system (WD-XRF: wavelength dispersive X-ray fluorescence spectrometry)
• – an energy dispersive FRX system (EDXRF: energy dispersive X-ray fluorescence spectrometry)

ICP, short for “inductively coupled plasma,” is an analytical technique that measures the content of chemical elements present in a sample with a very high accuracy.

Typical usage:

• • – Major (mass percent) and trace (ppm) chemical element analysis (1ppm = 1 mg/kg = 1 gram/ton = 0.0001 mass %)
  • – The accuracy of the analysis for trace elements is on the order of a few ppm

ICP analysis consists of ionizing the sample, previously put into solution by acid digestion, by injecting it into a 6000°K argon (or helium) plasma torch. The atoms are thus transformed into ions. After ionization, the electrons of the ionized atoms return to the ground state, and emit a photon (light) whose energy or wavelength is characteristic of the element. The wavelengths of the different elements present in the sample are then separated, identified and their intensities measured by a spectrometer. The elemental concentration is then determined by comparison to a calibration using a standard. The only elements that cannot be measured by ICP are H, C, O, N and halogens.

Before the analysis by ICP, the sample must be pulverized then put in solution with a strong acid or a mixture of strong acids (concentrated nitric acid (HNO3), liquid bromine (Br2), concentrated hydrofluoric acid (HF), hydrochloric acid (HCl). Sulfates are determined by leaching the sample with 10% dilute hydrochloric acid to dissolve the sulfate minerals.

The induction furnace is a simple, fast, and highly accurate analytical method for analyzing total sulfur and carbon contents in ores, rocks, soils, oils, cements, rubber, ash, and all other solid materials.

Typical Use:

• • – Determination of total S and C in ores and mine discharges (check if a mine discharge meets environmental standards)
  • – Determination of total S and C in soils for agriculture
  • – Concentrations analyzed can range from ppm to percent

Analysis of total sulfur and carbon in an induction furnace is based on combustion of the sample at a temperature up to 1550°C. Combustion is produced by adding gas pedals (iron, tin, and tungsten) and a flow of oxygen (O2) to the sample, placed in a porcelain crucible, which converts the sulfur in the sample to sulfur dioxide (SO2) and the carbon to carbon dioxide (CO2). Quantification of C and S is done by infrared spectroscopy, which relies on the infrared radiation absorbance properties of the gases generated by combustion. Each gas absorbs a specific wavelength of infrared radiation. The rate of absorption of the radiation depends on the concentration of these two elements in the gas generated by combustion. Some devices also allow the analysis of nitrogen.