Regulation of mechanical damage of filling body with sulfur based on coagulation and retarding technology

There are more than 900 pyrite mines in China, producing 13.2 million tons of pyrite annually.Sulphidic tailings are produced in the development of sulfur resources.Sulphidic tailings pose a serious threat to regional ecology when they are stored on the surface.Therefore, the cemented backfill technology is an effective approach for sulphidic tailings disposal which can avoid environmental contamination and safety problems.However, the filling body prepared from sulphidic tailings often has problems of cracking, crushing and strength failure, and the mechanism of strength development of backfills using sulphidic tailings is unclear.For the special development of the mechanical performance of cemented backfill prepared from sulphidic tailings, the mechanics evolution process was quantitatively studied by means of the setting time observation, the strength measurement and X-ray diffraction analysis.On the basis of the previous results, a new way was proposed to improve the mechanical performance of sulphide-rich backfills.It is revealed from the results that with the increase of sulphide content in tailings, the setting time was extended and the compressive strength decreased, with the 28-day strength degradation damage occurred.This could be ascribed to the oxidation of sulphide in tailings, during which process acid and sulphate were produced.As a result, hydration products dissolved and sulphate attack happened, leading to strength decreases.In the XRD patterns, a certain amount of secondary gypsum and ettringite crystals can effectively fill the pores in the filling body, which is conducive to the development of strength.However, large amounts of secondary gypsum and ettringite were found, which caused high inner pressure in backfill samples, thus leading to expansion cracks.The setting time of sulphide-rich backfills could be decreased by 15% and the early strength increased by two-fold with promoting coagulation technology, but the later strength deterioration is unable to restrain.However, the retarding technology can inhibit the hydration of C3S, and the formation of hydration products C—S—H gel and calcium hydroxide is delayed, and the mid-age strength could be improved by 35%.