New trends in enhancement of the efficiency of magnetic separation of magnetite ores

Abstract

In the processing of magnetite ores, in most cases the quality of the concentrate is enhanced and the losses of metal with the tailings are reduced by further complicating the beneficiation procedure: the number of crushing and magnetic separation stages is increased and the magnetic products are subjected to desliming.This complication of the procedure involves improvement of the beneficiation plant. Recent designs employ rod mills measuring 4.5 x 6 m (85 m 3) instead of 3.2 x 4.5 m (32 m~). The size of the magnetic separators has been increased. Wet magnetic separators with drum diameter 600 mm (167-SE, 26-SB) have been replaced by PBM-4 and 209-SE separators with drum diameter 800 and 900 n~n.Separators with drum diameter 1200 mmhave been introduced at the Lebeda State Beneficiation Combine. All these measures are intended to improve the magnetic beneficiation efficiency and the output and reduce the losses of metal with the tailings.However, the economic benefit obtained from complication of the procedures and enlargement of the plant for magnetic beneficiation of magnetic ores is much less than the cost of modernizing the production. Furthermore, the enhanced fineness of ore grinding reduces the magnetic susceptibility of the ferromagnetic particles and sharply increases their coercive force. This leads to losses of magnetite with the tailings and creates additional difficulties in the finishing of the magnetic products.Recently the Uralmekhanobr Institute has developed new ways of enhancing the efficiency of magnetic beneficiation of magnetite ores.From the thoery of magnetism [i] it can be shown that magnetization of ferromagnetic substances is a dynamic process and that complete magnetization does not occur instantaneously but only after the magnetic field has been applied for a certain time. Depending on the structure of the ferromagnetic material, the increase in magnetization may last several seconds, whereas the effect of the magnetic field on the ore particles in a magnetic separation plant is 0.3-0.5 sec, i.e., in the case of magnetic separation we use virtually instantaneous magnetization (with t * 0). The ratio of the magnetization I t , o at the moment the field is I'~~ depends on the nature of the substances applied to the total magnetization Ima x K --T~a x # and its ferromagnetic component content, and on the coercive force. For example, for Severopeschansk ores, which have an iron content of 50% and a coercive force of 35 Oe, this ratio is 0.90. But for the magnetic product of Kachkanar ores, which also contain 50% of iron but have a coercive force of 104 Oe, K = 0.88. For the initial Kachkanar ore, with an iron content of about 16%, it is even lower (0.65).Thus whereas in the processing of rich magnetically soft ores the time required to attain almost total magnetization is reached even within the working zone of the separator, for lean magnet~cally hard ores, like Kachkanar titanomagnetites, the magnetization time, and therefore the separation time, must be increased.In beneficiation plant...