Alkaline hydrothermal activation of molybdenum tailings to prepare one-part geopolymer: Activation mechanism and strength

Molybdenum tailings (MT) are solid waste from molybdenum ore beneficiation, which can cause environmental pollution when stored in tailings ponds for a long time. The use of alkaline hydrothermal activation to improve the low reactivity of MT as an active precursor to one-part geopolymers is a novel way to resource MT. This paper evaluates the feasibility of alkaline hydrothermal activation of MT and investigates the mechanical properties of the activated MT base polymer prepared by a one-part method. The results showed that alkaline hydrothermal activation greatly promoted the dissolution of silicon in MT, weakened the crystal properties of quartz phase in MT and destroyed the original structure of MT. The amorphous sodium aluminosilicate on the surface of activated MT dissolves in water and provides an alkaline environment for the geological polymerization reaction. Combined with the analytical results of XRD and FTIR, the alkaline hydrothermal activation of MT was controlled by the optimal sodium hydroxide solution concentration, activation temperature and activation time of 5 M NaOH, 200 °C and 4 h, respectively. Based on this, the one-part geopolymer was prepared directly by adding water to activated MT 5-4-200 and slag, and the compressive strength can be improved. SEM and EDS results show that alkaline hydrothermal activation treatment renders inert MT reactive and the reaction product of activated MT and slag forming a one-part geopolymer is an amorphous C(N)A-S-H gel.