Design of Comminution Circuit for Optimum Performance of the Gravity Separation Unit at Itakpe Iron Ore Processing Plant, Nigeria

Abstract

Designing an efficient and economic mineral processing plant begins with the choice of the best and most economic comminution circuit based on ore properties and concentrate end-user’s specifications. This is because crushing and grinding for preparation of suitable feed for the downstream processes are cost intensive. The Itakpe iron ore processing plant presently produces a taiing material containing up to 22% iron minerals mostly fines produced inevitably during comminution. This article analyzed the existing circuit and ore properties, and presents specific comminution tests that were undertaken in order to recommend an alternate and more effective circuit. Sieve analyses of the various products of the existing circuit were carried out. The results show that fines exist in the circuit as a result of the brittleness of some portions of the ore which leads to crumbling and sloughing of the material during crushing and handling. It is revealed that mechanical stacking and reclamation also contributes to the generation of fines in the circuit. One possibility to a solution is to screen the product of secondary crusher ahead of grinding with a +2mm coarse screen between the reclaimer and the primary autogenous mills to prevent further production of fines during crushing unless the downstream recovery process is entirely designed for flotation. This option however still allows much fine material to the concentration lines. It is therefore recommended that materials less than 2mm be screened off the products of primary and secondary crushers and treated separately in gravity or magnetic unit without grinding. A +2mm screen is also recommended for installation as control for the product of primary autogenous mills which should be treated for concentration in the gravity unit. If flotation is to be employed, a regrind mill will be installed on either or both of the concentration lines or to a blend of the two. Keywords: sloughing, crumbling, user’s specifications, hardness, dropping impact, iron-rich, brittlenes