Synthesis and Characterization of Micaceous Iron Oxide Pigment from Oily Cold Rolling Mill Sludge

Oily cold rolling mill (CRM) sludge is a kind of solid waste produced in production process of cold rolled strip In China, more than one hundred thousand tons of oily CRM sludge is produced each year. The oily CRM sludge contains lots of valuable iron and alloying elements, along with plenty of hazardous organic components, which makes it an attractive secondary resource and an environmental contaminant at the same time At present, oily CRM sludge is mainly used as smelting raw materials Its direct re-use in sintering may lead to some problems because high oil content of oily CRM sludge results in increased emission of volatile organic compounds including dioxins and can lead to problems in waste gas purification systems, e.g glow fires in electrostatic precipitators. In this paper, micaceous iron oxide (MIO) pigment was synthesized from oily CRM sludge by means of the multi-step processes, including acid leaching, preparation of the ferric hydroxide precursor and hydrothermal synthesis. The experimental conditions, including NaOH concentration and hydrothermal reaction temperature were investigated in order to determine the optimal ones. The morphology and particle size of as-prepared MIO pigment were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that the obtained pigment had high purity (∼98.7%) and good oil absorption (∼18.8%). The synthesized MIO pigments met the required characteristics of MIO pigments for paints (ISO10601-2007). MIO pigments synthesis method presents a viable alternative for oily CRM sludge recycling.