The Development of a new Low Cut Point Spiral for Fine Coal Processing

Abstract

Records show that Spirals, for the separation of heavy minerals, existed over 100 years ago and have continued to undergo development ever since. Applications of spirals to fine coal (between 1.00 mm and 100 micron) are relatively more recent dating back approximately 30 years. The advantages of spirals are well recognised within the coal industry and include simplicity of operation, reliability, a high tolerance to variation in operating conditions along with low capital and operating costs. A limiting feature of conventional coal spirals is an inability to achieve d50 cut points at specific gravities (sgs) lower than 1.65. With technological advances in coarse coal treatment enabling lower cut points, this limitation of coal spirals in fine coal treatment has become increasingly more significant in the context of overall plant performance. Mineral Technologies has addressed this limitation and recently developed the LC3, a new coal spiral capable of separation cut points lower than those of other available models. Extensive testing occurred during the design and development stages and the LC3 readily achieved cut points in the specific gravity (sg) range 1.40 to 1.55. The design of the LC3 is a clear departure from other current coal spirals. It entails continuously variable profiles and pitches and is based around reducing turbulence to enhance subtle separating mechanisms. Initially developed as an 8-turn unit, it is however no taller than other industry-accepted 7 turn models. A 4-turn format LC3 has also now been developed. As well as achieving lower cut points at higher than expected unit loadings, preliminary testing also indicates comparable or better separation efficiencies at conventional cut points and, additionally, a potential for separating particles at sizes previously deemed too fine for spiral applications. This paper presents test data and findings from the development program and subsequent, post-development investigations such as a 2-stage (middling retreat) circuit.