Competitive crystallization of B, Si, and Mg and two-stage separation of olivine and suanite from boron-bearing slag in supergravity field

Abstract

Boron-bearing slag is a typical secondary resource of boron (B) and magnesium (Mg). However, the boron dispersed in the amorphous phase, which is difficult to recover from the boron-bearing slag. This study investigated the effect of supergravity field on the competitive crystallization behavior of B, Si, and Mg in boron-bearing slag, and developed an efficient method for two-stage separation of olivine (Mg2SiO4) and suanite (Mg2B2O5) from the slag. In stage 1, the Mg2+ was preferentially crystallized into olivine with the SiO44- rather than B2O54- at 1623 K to 1473 K, and the olivine crystals were efficiently separated from the boron-bearing slag melt under the supergravity field. Due to the separation of olivine in the stage 1, the SiO44- was depleted and a favorable condition for single crystallization of suanite was created in the remaining boron-rich slag. Thus in stage 2, the B2O54- and Mg2+ were adequately crystallized into suanite at 1473 K to 1323 K, and the suanite crystals were recovered further from the separated boron-rich slag melt in the supergravity field. Moreover, the high purity and high crystallinity of the suanite and olivine separated from the boron-bearing slag confirmed the enhancement of supergravity field on the solid-liquidseparation in a complex slag system.