Abstract
The cemented phosphogypsum (PG) backfill technique provides a new method for massive consumption of PG, and therefore alleviating the environmental pollution of PG. This study considered the effects of slurry preparation on the performance of cemented PG backfill. A L16(44) orthogonal experiment was designed to analyze four factors, namely the solid content, phosphogypsum-to-binder ratio (PG/B ratio), stirring time and stirring speed, with each factor having four levels. According to the range analysis, the solid content played the dominant role in controlling the bleeding rate, while the setting times strongly depended on the PG/B ratio. In terms of strength development of the backfill, the PG/B ratio was shown to be the most significant factor determining the unconfined compressive strength (UCS), followed by the solid content, stirring time and stirring speed. Furthermore, the results showed that the slurry preparation affected the environmental behavior of impurities that originated in PG. By analyzing the concentrations of impurities in the bleeding water of the slurry as well as the leachates of the tank leaching test, the results showed that the release of F− and SO42− was aggravated clearly with the increase in the PG/B ratio, while the release of PO43− always remained at relatively low levels.
Highlights
In the phosphate industry, phosphoric acid is usually extracted from phosphate ore by using concentrated sulfuric acid, leaving a by-product of phosphogypsum (PG) which is mainly composed of CaSO4·2H2O
The unconfined compressive strength (UCS) of samples cured for 28 d ranged from 0.74 MPa to 2.26 MPa
These results indicate that the slurry preparation conditions have significant effects on the cemented PG backfill, including both properties of slurry and the strength of hardened backfill
Summary
Phosphoric acid is usually extracted from phosphate ore by using concentrated sulfuric acid, leaving a by-product of phosphogypsum (PG) which is mainly composed of CaSO4·2H2O. Besides CaSO4·2H2O (>90%), PG contains some impurities such as phosphate (PO43−), fluoride (F−), organic matters, heavy metals and radioactive components [4,5,6,7]. These minor compounds have caused serious environmental pollution at storage sites [8,9], and hindered the reuse of PG, and only 15% of PG is recycled worldwide [10,11]. It has been estimated that about 60% of PG generated could be consumed by using PG as the aggregates in the backfill process [12]. In the cemented PG backfill process, the PG together with the hydraulic binder, water and some additives were mixed homogeneously to form a slurry on the land surface, and the prepared slurry was transported
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