Settling characteristics of coal washery tailings using synthetic polyelectrolytes with fine magnetite

In the coal preparation plant, the run of mine coal undergoes a series of operations, including washing, wet screening, sedimentation and dewatering. The process requires the circulation of large volumes of water from which large volumes of waste water containing a variety of solid particles are generated. Clarification of the tailing water is often carried out in a thickener by adding suitable polymeric flocculants. The main objective of the clarification is to obtain clear water with a low turbidity value. It is important to produce good quality recirculation water for the smooth operation of the plant, otherwise the presence of suspended and dissolved solids in the wastewater can lead to a reduction in the efficiency of the washing process. Waste waters produced from coal preparation plants contain high percentages of ultrafine particles and inorganic impurities, which are composed of clay minerals such as kaolinite, illite, muscovite, quartz, and coal particles. The natural sedimentation rate of these particles present in colloidal and finely divided suspended form is very slow. Flocculation technology is applied in most coal preparation plants to recover water from the tailings of coal washing operations. The flocculation is accomplished through the use of inorganic salts, polymeric flocculants or both, depending on the chemical and physical characteristics of the pollutants present in suspended and dissolved states1. Synthetic or natural polymeric reagents are generally used as flocculating agents in most coal preparation plants. Synthetic polymers are comparable to natural polymers due to their use in small quantities for the separation of solids from liquids. In order to achieve the faster settling rate, the optimization of process parameters such as suspension pH, polymer type and dosage are very important to achieve the desired settling rate and the water clarity values. Various flocculant combinations, viz. cationic, anionic, non-ionic have been used to achieve the highest settling rate with lowest turbidity2–4. In this investigation, the clarification of waste water was carried out by the incorporation of a suitable reagent together with fine magnetic material known as magnetic carrier technology. Magnetic carrier technology is an innovative way of selectively manipulating fine particles in suspensions by coating them with a magnetic species. It utilizes the physical, chemical and surface properties of a magnetic carrier to enable selective attachment with the desired particles. The selective increase in floc formation and faster settling rates with magnetic response of the particles are achieved by incorporating a strongly magnetic phase. The negatively charged impurities such as clay, bacteria, viruses and colour present in Settling characteristics of coal washery tailings using synthetic polyelectrolytes with fine magnetite