From performance to mechanism: Analysis of controlling strength attenuation of high-sulfur lead-zinc tailings cemented paste backfill

Abstract

The disposal of high-sulfur tailings severely impacts the environment. Preparing them into cemented paste backfill (CPB) and backfilling them into underground goafs is an environmentally friendly technology. However, the study on high-sulfur CPB performance and control mechanism is currently unclear, resulting in application limitations. This study comprehensively studies the rheological and mechanical properties, control methods, and environmental evaluation of high-sulfur CPB. The results indicate that the higher the sulfur content, the higher the shear yield stress and viscosity, and the better the flowability. However, the initial and final setting times are prolonged, and the strength shows a trend of increasing, decreasing, and increasing with the extension of curing time, indicating that the strength attenuation is obvious. By adding different inhibitors to high-sulfur CPB, it was found that naphthalene superplasticizer (FDN) has the best inhibitory effect on strength attenuation. The oxidation of pyrite, which produces SO₄²⁻ and H⁺, is a key cause of strength attenuation. Different inhibitors boost strength mainly by curbing pyrite oxidation. They also enhance compactness by increasing the amounts of hydration products like calcium silicate hydrate (C-S-H), Ettringite (Et), and gypsum to fill pores. The strength control mechanism of the inhibitor mainly has two ways: to accelerate the formation of C-S-H and to promote the amount of Et. FDN in mitigating strength attenuation and achieving high immobilization rates for Pb²⁺ (92.2 %) and Zn²⁺ (98.9 %). This study has practical value for the environmental protection and utilization of CPB prepared from high-sulfur tailings, solving the problems of strength attenuation in high-sulfur CPB and providing new ideas for the treatment of high-sulfur tailings.