The Formation Process and Mechanism of Total Activated Potassium During the Preparation of Si–Ca–K–Mg Fertilizer from Molybdenum Tailings

Silicon–calcium–potassium–magnesium fertilizer (Si–Ca–K–Mg fertilizer), a critical acidic soil conditioner for remediating polluted acidic soils, encounters a significant challenge: substantial potassium loss through flue gas during high–temperature calcination, which increases production costs. This study optimized the blending ratio of molybdenum tailings (MTs) with CaCO3 and CaSO4, systematically investigating the interplay between clinker–soluble potassium, volatile potassium loss, and total activated potassium content during calcination. Key findings include the large–scale utilization of molybdenum tailings; a mass ratio of mMTs:mCaCO3:mCaSO4 = 1:0.5:1.0 leads to a total activated K2O content of 3.05 wt.%. Enhancing nutrient efficiency by increasing the proportion of additives (with a mass ratio of 1:0.7:0.4) results in a total activated K2O content of 4.50 wt.%, which is 1.5 times the national standard. Mechanistically, calcination decomposes potassium feldspar (K–feldspar) in the tailings into leucite and SiO2. CaO derived from CaCO3 reacts with SiO2 to form calcium silicate, facilitating the decomposition of leucite into water–soluble kaliophilite. Simultaneously, thermal diffusion promotes the ion exchange between Ca2+ of CaSO4 and K+ of feldspar and leucite, thereby forming potassium sulfate. However, part of this potassium sulfate, along with some water–soluble kaliophilite, volatilizes at high temperatures, contributing to flue gas loss. Recycling the lost potassium back into fertilizers enables complete potassium utilization. This work establishes a robust framework for efficiently producing Si–Ca–K–Mg fertilizer from molybdenum tailings, addressing key challenges in potassium retention and resource recycling during industrial synthesis.