Liquid-Liquid extraction inductively coupled plasma atomic emission spectrometer (ICP-AES) for determination of elemental sulfur in carbonate rock

Under condition of hypoxia, sulfate sulfur is reduced to sulfide sulfur in the process of carbonate deposition. Part of the sulfide is combined with organic to generate complicated organic sulfur while the majority of sulfide with metal ions to form sulfide precipitation. However, the sulfide precipitation is so unstable that can be converted to a stable pyrite through hydrogen sulfide, iron sulfide polysulfide and ferrous sulfide paths. Under the oxygen-rich condition, the sulfur-oxidizing bacteria will oxidate sulfide into elemental sulfur and the disproportionation of elemental sulfur will lead to the formation of various sulfurs which are stored in carbonate deposition.At present, a variety of methods are available for the measurement of elemental sulfur and its species. Unfortunately, only a few are useful at mg/L levels, which offer the possibility of applying them in different matrices. There are methods for the determination of elemental sulfur at trace levels, but they are often complicated and/or time-consuming. As a new analytical technique, inductively coupled plasma atomic emission spectrometry (ICP-AES) has many advantages such as high sensitivity, small matrix effects, wide linear range, good precision and a variety of elements can be measured simultaneously. In this paper, a method is proposed to analyze elemental sulfur in carbonate rock, which is determined with ICP-AES at the wave length of 180.7 nm and 182.0 nm, respectively. The linear correlation is 0.999 and the relative standard deviation (RSD) is lower than 5.0%.In this work, the pre-treatment method of the elemental sulfur in carbonate is established. We made efforts to reduce the impacts of extraction volume, ultrasonic time and digestion time on the recovery of elemental sulfur to obtain the optimal solution for elemental sulfur extraction. The optimal scheme is as follow, firstly, a 0.5 g carbonate standard sample was weighed in a 20 mL glass tube, followed by adding 5 mL hexane rapidly, 10 min of ultrasonic，intermittent 5 min, repeating two times and 30 min of cumulative ultrasonic, then stewing the filtrate for 10 min stratification. After centrifuging for 10 min, we got a supernatant and then transferred it to a Teflon crucible. They were repeated two times. Then hexane supernatant was collected and evaporated to dryness at a low temperature, 2 mL purity nitric acid was added to the Teflon crucible, then the lid cover was fixed to the cylinder barrel and then the solution was digested in an oven for 5 h at 150 ℃. Next we set the volume to 25 mL, shaking and measuring. We also conducted the blank experiments and standard addition method to obtain the recovery of elemental sulfur at 90%-110%.The results indicate that this method can meet the test requirements and can be used to determine elemental sulfur in carbonate rock.