ENRICHMENT OF THE MANGANESE CONTENT BY WET HIGH INTENSITY MAGNETIC SEPARATION FROM CHIKLA MANGANESE ORE, INDIA

Manganese ores by and large are low and medium grade types and need beneficiation to utilise them in ferromanganese industry. Isodynamic separation followed by chemical characterisation of ores from this region indicated their susceptibility to Mn enrichment. Details of characterisation, heavy media and magnetic separation studies carried out on a medium grade manganese ore, containing 44% Mn, 7.8% Fe and 22% acid insolubles, from the Chikla region are presented. By processing the material on a wet high intensity magnetic separator, a product with 51% Mn at 95% recovery could be obtained.


INTRODUCTION
The estimated in-situ reserves of the manganese ores in India are of the order of 370 million tonnes, with recoverable reserves of about 177 million tonnes [1]. The grades suitable for various industries and the total manganese ore reserves are given in Table I. The domestic consumption pattern of manganese ore during 1990-1993 is given in Table II. The major manganese ore consumption is by ferroalloys and iron and steel industries in the country. Out of the 24 ferromanganese units in the country, 10 units are in the organised sector and the rest Corresponding author.   [2]. The location, capacity and the grade of manganese ore being used in the 10 units of the organised sector [3] is given in Table III. The manganese ore requirement for the iron and steel industry is assessed at 1.065 million tonnes, based on the envisaged hot metal production target of 21.3 million tonnes by nine major pig iron plants. The blast furnaces of the steel plants in India consume manganese ore with 25-30% Mn, 5-25% SiO2, 5-8% A1203, 14-26% Fe and 0.074-0.34% P and do not face any serious problem due to availability of adequate ore meeting the above specification. WET  (MOIL) to exploit manganese ores from many of these deposits. This paper deals with the characterisation and beneficiation of manganese ores from Chikla deposit, of Maharastra (Fig. 1). The manganese formation of Chikla belongs to the Sausar group of rocks of Archaean age. In-depth mineralogical, petrological, genesis etc. are reported elsewhere on the ore bodies of Chikla [4,5,6]. The paper describes the chemical characteristics of low and medium grade manganese ores drawn from Chikla and the beneficiation studies carried out on a medium grade ore sample at the instance of MOIL.

CHARACTERISATION STUDIES
The manganese ore samples in bulk quantities were collected from various levels of the Chikla mine. The mineralogical investigations were carried out with optical microscope (Leitz-ortho plane), X-ray diffraction (Philips diffractometer) and scanning electron microscopy (Jeol, JSM 35 CF with WDS attachment). The samples were classified into various sieve fractions and each fraction was subjected to magnetic separation using isodynamic magnetic separator (with 20 side tilt, 30 forward slope and with the current of 0.8 A). All the magnetic products of various size fractions were analysed with the help of XRF (Philips, for Mn, Fr, Si, As, P, S, Ti, Ba, Mg) and flame photometer (systronics model K-111, for Na, K, and Ca) to determine the metal distribution pattern. The details are reported elsewhere [7]. However, the metal  distribution pattern in low and medium grade ores are shown in Table IV. Subsequent to these investigations, another medium grade manganese sample from the Chikla region was received from MOIL to study its amenability to beneficiation. The ore was jaw and roll crushed (at 3 mm rolls gap) and a representative sample was drawn for wet sieving, heavy medium and magnetic separation studies. The weight and the Mn and Fe distribution in various size fractions.of the roll crushed material are given in Table V. HEAVY MEDIA STUDIES Various size fractions of the roll crushed material were subjected to sink and float test using an organic liquid, tetrabromoethane of specific gravity 2.96. The heavy and light fractions were collected after washing them thoroughly with acetone and water. All the heavies and light fractions were weighed (Table VI) but not analysed for Mn and Fe, since only 6% of the material resulted as the overall light fraction.

MAGNETIC SEPARATION STUDIES Wet Low Intensity Separation
The roll crushed manganese ore was ground to below 100 tm size and the ground ore was treated on SALA wet low intensity drum magnetic  separator. The magnetic and non-magnetic products were collected. The non-magnetic fraction was processed once again and the magnetic fraction thus obtained was considered as middling. The three products obtained on SALA low intensity magnetic separator were analysed for Mn and Fe (Table VII).

Wet High Intensity Magnetic Separation
The roll crushed material was further crushed by keeping the minimum possible gap between the rolls and from the resulting product a representative sample was drawn and subjected to magnetic separation on BOXMAG wet high intensity magnetic separator at 12,000 G. The roll crushed material was further ground to 30 and 60 min and this ground material was processed on wet high intensity magnetic separator. All the magnetic and non-magnetic products were analysed for Mn and Fe (Table VIII).
Another set of studies was carried out on this ground product by varying the intensity, so as to ascertain the optimum conditions and the products were analysed for Mn and Fe (Table IX).

RESULTS AND DISCUSSION
The high grade material suitable for ferromanganese production is limited (Table I), although the country has vast resources of the manganese ores. The ferromanganese industry in the country is likely to be affected due to this and it calls for an urgent need to augment the ferromanganese grade reserves. In Maharastra MOIL operates manganese mines both open cast and underground mining. The manganese ores mined from Chikla region contain mostly low grade to medium grade type ores. Mineralogical studies on various grade ores drawn from Chikla revealed the presence of manganese minerals in three predominant forms: manganese oxides, manganese silicates and as manganese carbonates, while iron is present as hematite and goethite. Braunite, bixbyte, husmannite, jacobsite and coronadite form the major primary oxides, while pyrolusite, cryptomalene and psilomalane are recorded as secondary oxide minerals. The manganese silicate phases are represented by hedenbergite, spessartite and rhodonite while kutnohorite and rhodocrosite form the carbonates. The gangue minerals mainly include silicates, carbonates, phosphates and sulphate. The silicate minerals occur in a close association with the manganese minerals. The XRD pattern of a medium grade ore sample is illustrated in Fig. 2. Quartz, orthoclase, plagioclase and diopside together form a major portion of the gangue minerals. Calcite and barite appear to be associated with manganese and silicate phases. Calcite occurs as secondary veins. Electron microscopic studies through X-ray image mapping revealed these veins to be rich in phosphorus. The phosphorus content in the ores from Chikla is relatively low and well within the range needed by ferromanganese industry. However, minute grains of manganese minerals within silicates and similar silicate grains within manganese phases pose problems in their liberation.
The distribution of different elements in various size fractions in low grade (Table IVa) and medium grade (Table IVb) Table IV. These samples were subjected to isodynamic separation and the magnetic products of corresponding fractions were analysed. The analyses indicated substantial improvement in the quality of the magnetic fractions which is largely due to the rejection of silica and calcia content, in addition to the high magnetic susceptibility of the manganese bearing minerals like braunite, bixbyte and husmannite. As the major gangue minerals are quartz and calcium carbonates, the enrichment of manganese by magnetic separation technique may be the ideal process to upgrade the manganese ores of Chikla region.
Another medium grade ore sample (44% Mn, 7.7% Fe, with 20-22% acid insolubles) from the Chikla region was studied for its amenability to beneficiation at the instance of MOIL. The preference of MOIL is to study its response to beneficiation by jigging. Table V indicates the distribution pattern of Mn and Fe in various sieve fractions of the roll crushed material (3 mm rolls gap). The sink and float studies on the size fractions using tetrabromoethane reveal (Table VI) that only 6-7% of the material could be obtained as light fraction which means 6-7% of the material only can be rejected theoretically by jigging. In case the material is subjected to jigging the manganese content can only be raised to around 47% Mn, as against the theoretical possibility of around 55% Mn by rejecting the 20% acid insolubles. Hence the application of jigging to such ores is not considered as a pragmatic approach.
It can be seen from Table VII that the manganese minerals are not prone to enrichment by wet low intensity magnetic separation on SALA drum magnetic separator. As the isodynamic separation studies on a similar medium grade ore revealed its susceptibility to the manganese enrichment, studies were carried out on BOXMAG wet high intensity magnetic separator. Table VIII indicates the possibility of enriching the Mn content to around 51% with 85% recovery. However, the ore needs to be ground to below 100 gm size. Studies carried out by varying the field strength revealed that around 15,000 G may be adequate to enrich the Mn content to around 51% Mn with 95% recovery, which is very close to the theoretically possible enrichment value. As the manganese ores from the Chikla region are the low phosphorus bearing ores, the beneficiated ore can be a potential resource for the ferromanganese industry.

CONCLUSIONS
The manganese ores from Chikla region are by and large of low to medium grade type and low in phosphorus content. Isodynamic separation studies on various ores from this region revealed their susceptibility to high intensity magnetic separation due to the presence of some manganese oxide minerals (bixybite, braunite, husmannite) along with quartz and calcite as major gangue.
The characterisation and beneficiation studies on a medium grade manganese ore sample from Chikla containing 44% Mn, 7.9% Fe and 20-22% acid insolubles revealed that the manganese content can be raised to around 47% Mn by jigging, whereas by grinding the ore to below 100 lam size followed by treatment on wet high intensity magnetic separator the Mn content can be enriched to 51% Mn with 95% recovery. This material having Mn/Fe ratio 5.7 with low phosphorus can be a potential resource for the ferromanganese industry.