Ultrasound-assisted extraction for total sulphur measurement in mine tailings

► We develop a total sulphur measuring procedure of mine tailings. ► Ultrasound is used in the sample pre-treatment process. ► Full factorial design is applied to identify the best level of effecting factors. A sample preparation method for percentage recovery of total sulphur (%S) in reactive mine tailings based on ultrasound-assisted digestion (USAD) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) was developed. The influence of various methodological factors was screened by employing a two-level and three-factor (23) full factorial design and using KZK-1, a sericite schist certified reference material (CRM), to find the optimal combination of studied factors and %S. Factors such as the sonication time, temperature and acid combination were studied, with the best result identified as 20min of sonication, 80°C temperature and 1ml of HNO3:1ml of HCl, which can achieve 100% recovery for the selected CRM. Subsequently a fraction of the 23 full factorial design was applied to mine tailings. The percentage relative standard deviation (%RSD) for the ultrasound method is less than 3.0% for CRM and less than 6% for the mine tailings. The investigated method was verified by X-ray diffraction analysis. The USAD method compared favorably with existing methods such as hot plate assisted digestion method, X-ray fluorescence and LECO™-CNS method.