Optimization of digestion parameters for analysing the total sulphur of mine tailings by inductively coupled plasma optical emission spectrometry

Abstract

The oxidation of sulphidic mine tailings and consequent acid generation poses challenges for the environment. Accurate and precise analysis of sulphur content is necessary for impact assessment and management of mine tailings. Here, the authors aim at developing a rapid and easy digestion procedure, which may analyse and measure the total amount of sulphur in mine tailings by using inductively coupled plasma. For evaluating effects of several variables, the researchers used a univariate (analysis of variance (ANOVA)) strategy and considered factors such as composition of the acid mixture, heating time, and refluxing device to optimize the performance. To do the experiment, the researchers have used two certified reference materials (KZK-1 and RTS-2) and samples of tailings from Musselwhite mine. ANOVA result shows that heating time is the most influencing factor on acid digestion of the reference materials whereas in case of a digestion of tailings sample, hydrochloric acid proved to be the most significant parameter. Satisfactory results between the measured and referenced values are found for all experiments. It is found that the aqua regia (1 ml HNO(3) + 3 ml HCl) digestion of 0.1 g of samples after only 40 min of heating at 95°C produced fast, safe, and accurate analytical results with a recovery of 97% for the selected reference materials.

Ultrasound-assisted extraction for total sulphur measurement in mine tailings

“…Prior to testing, tailings were air dried for 24-48 h and placed in an airtight sealed pack. The analysis of particle size distribution showed that the tailings contain mainly fine solids, with D 50 0.015 mm [22] and 97% of solids are finer than 74 m (passing #200 sieve).…”

“…Standard reference material RTS-2 (S = 18.95 wt.%) was used for calibration. Hot plate digestion followed by ICP-OES analysis of total sulphur was done according to procedure described by Alam et al [22]. In addition, the X-ray diffraction (XRD) data were obtained using a Rigaku-MiniFlex II, powder diffractometer (Japan), using CuK␣ ( for K␣ = 1.54059Å) over the desired 2Â range with a step width of 0.05 • .…”

“…Mix the CRM (KZK-1) thoroughly, as well as mix tailings thoroughly to achieve homogeneity before weighted in separate tests. One hundred milligrams (100 ± 1 mg) of sample mass is considered the suitable amount for accurate total sulphur measurement [22]. The sample was then placed in a digestion tube.…”

“…Table 3 contains the coded values of high and low levels for the 2 3 full factorial design matrixes (Experiments 1-8) for CRM. The amount of HNO 3 was fixed to 1 ml [22] throughout the experiment and the amount of HCl was varied to 1 ml and 3 ml according to the 2 3 factorial design matrixes. All experiments were carried out in triplicate (n = 3) and the average of total sulphur percentage, percentage recovery of total sulphur (denoted here after as %S), Percentage of relative standard deviation (%RSD) and the percentage of error are shown in the same table.…”

“…Elemental analyzers are also found unsatisfactory for total sulphur analysis from mine tailings and soil samples [21]. A recent study on total sulphur measurement of mine tailings by Alam et al [22] has further advanced the technology. A 40-min hot plate digestion at 95 • C temperature with aqua regia (1 ml HNO 3 + 3 ml HCl) for 0.1 g of reference materials (KZK-1 and RST 2), have yielded 97% recovery of total sulphur by ICP-OES technique, which is so far the most accurate and fastest method for the total sulphur analysis of mine tailings.…”