熔融氧化镍渣连续冷却过程磁铁矿晶体析出长大行为研究

Study on the precipitation and growth behavior of magnetite crystal during continuous cooling of molten nickel oxide slag

摘要:

镍渣中铁元素的高效提取一直是镍渣高效高值化再利用关注的热点。本文利用Factsage软件对熔融氧化镍渣中磁铁矿晶体的形成及优先选择性析出行为进行预测,然后采用高温激光共聚焦显微镜(HT-CLSM)对熔融氧化镍渣连续冷却过程中磁铁矿晶体的析出长大进行原位观察,对比研究了5~50 ℃/min冷却速率下磁铁矿晶体的生长过程,通过SEM-EDS、XRD、ICP手段对观察样品的形貌、物相和成分进行表征。结果表明,熔融氧化镍渣连续冷却过程磁铁矿晶体会从熔体中优先选择性析出,初始析出温度在1430~1450 ℃之间。较低的冷却速率(5~15 ℃/min)下,晶体初始形核析出较慢,晶粒在1200~1400 ℃稳定生长,平均生长速率可达0.141 μm/s,最终晶粒尺寸超过100 μm；较高的冷却速率(25~50 ℃/min)可以促使磁铁矿晶体在生长初期迅速形核并析出,但稳定生长速率较小,最终晶粒尺寸在20~30 μm范围。

Abstract:

The efficient extraction of iron from nickel slag have attracted more recent attention in the recycling of nickel slag. In this paper, FACTSAGE software was used to predict the formation and preferential precipitation behavior of magnetite crystal in molten nickel oxide slag. The precipitation and growth of magnetite crystal in molten nickel oxide slag during continuous cooling were in-situ observed by high temperature laser confocal microscope (HT-CLSM), and the growth characteristics of magnetite crystal under 5~50 ℃/min cooling rate was studied. The morphology, phase and composition of the samples were characterized by SEM-EDS, XRD and ICP. The results show that magnetite crystals are preferentially precipitated from the melt during continuous cooling, and the initial precipitation temperature is between 1430~1450 ℃. At low cooling rate (5~15 ℃/min), the initial nucleation and precipitation of the crystals are slow, and the grains grow stably at 1200~1400 ℃, with an average growth rate of 0.141 μm/s, the final grain size is more than 100 μm. High cooling rate (25~50 ℃/min) can promote the rapid nucleation and precipitation of magnetite crystal at the initial stage of growth, but the stable growth rate is small, and the final grain size is 20~30 μm.