Research on the mechanism of P and F in phosphogypsum stabilized by humic acid synergized with group metallic triad-based curing agent

Abstract

The high levels of soluble phosphorus (P) and fluorine (F) in phosphogypsum (PG) pose a significant environmental challenge to the sustainable development of the P chemical industry. In this research, we present a green and low-cost stabilization strategy that employs a synergistic combination of organic and inorganic additives to effectively suppress the release of P and F from PG. Through batch experiments, we systematically evaluated the effects of humic acid (HA) synergized with inorganic curing agents on the leaching behavior of contaminants, with a focus on their impact on pH and immobilization efficiency of P and F. The optimal formulation consisted of 5 wt% type-II humic acid (HA-2) combined with 1 wt% type-II group-synergistic metallic triad-based curing agent (GMT-2). Under simulated leaching conditions representative of surface and groundwater exposure, this material yielded a leachate with a pH of 5.51, P concentration of 0.1 mg L⁻¹, and F concentration of 0.9 mg L⁻¹, which complies with China's class III surface water quality standards (GB 3838-2002). The underlying stabilization mechanisms of the combined system leverage physical coating, chemical precipitation, and a distinctive bridged ternary complexation mechanism to construct a denser and more stable immobilization layer on the PG surface, in which the integrated approach achieves a durable synergistic fixation of P and F. This work provides a practical method for the environmentally sound management and sustainable utilization of PG.