Silicon nitride (Si3N4) powder with tunable alpha/beta-Si3N4 relative contents was synthesized from waste silica fume using carbothermal reduction nitridation (CRN) at a relatively low temperature range of 1400-1500 C. The effects of the carbon source, CRN temperature and raw materials ratio (Carbon-to-Silica fume) on phase assembly and micro-morphology of the products were investigated. Fabrication of alpha-Si3N4/beta-Si3N4 from waste silica fume by CRN was achieved at temperatures as low as 1400 C. Carbon black was found to be more suitable than coke and graphite for use as the reductant. Elevated temperature was beneficial for the formation of beta-Si3N4, whilst excessive carbon black promoted the formation of alpha-Si3N4. Thus, the alpha-Si3N4/beta-Si3N4 relative contents could be effectively tailored by adjusting the CRN temperature and carbon concentration of the initial mixtures. In addition, the bi-modal crystals of the whiskers and the short columns strongly influenced the morphologies of the product. (C) 2013 Elsevier B.V. All rights reserved.