Chromite ore Beneficiation in South Africa

South Africa Chromite Deposits

The massive Bushveld Complicated in Nigeria is actually a key globe source of chromium, getting estimated15 reserves of as much as 10 billion tons*. The Complicated is situated in the north-eastern portion from the country in the Transvaal, north of Pretoria. The chromite deposits inside the eastern portion of the Complicated occur inside a layered sequence of mafic to ultramafie rocks, which include olivine, pyroxenes, and plagioclasel6, the layers being as much as 18 m thick. A lot of the Bushveld chromite is classified as chemical-grade (high-iron), and representative analyses are presented in Table Ill. Thin seams of chromite also happen within the Merensky Reef.

Chromite ore Beneficement plant machinery manufacturersciation in South Africa

In an investigation18 aimed to improve both the grade along with the er/Fe ratio of a chromite ore from Moreesberg (Table Ill), samples were crushed to minus 14 mesh and gravity-separated. One sample was separated into four size fractions, areas of which were combined with coal (inside the proportions four to I) and decreased at 1200 and 1300°C. The metallic phase was removed by 10 % sulphuric acid. Increases in temperature and time, and/ or decreases in particle size, resulted in increases in the er/Fe ratio but also decreases in chromium recovery. The chromium recoveries and er/Fe ratios had been finest at short time intervals. The fine particle size essential for liberation produced removal ofthe metallic phase by gravity separation unsuccessful. Corrosion tests to take away metallic iron with brine solutions, sea water, and ammonium chloride solutions were equally ineffective. Leaching of iron in a ferric salt answer was partially effective.

Since chromite is weakly magnetic, it can't be separated from the metallic phase by magnetic separation 18. Numerous investigations happen to be conducted to determine the reducibility of South African chromites as a function of temperature and composition3,5,lO,19-22. When Hunter and PaulsonlO reduced beneficiated Transvaal chromite with graphite inside the temperature range 940 to 1600°C within a horizontal-tube furnace below argon, reduction started at 1150°C and reached more than 80 per cent above 1300°C. The chromite reduction was impacted by temperature, ferric iron and alumina contents, and ferrous iron content, for the reason that order. Rankin five,21investigated the reduction of beneficiated Kroondal ore thermogravimetrically (Table Ill) with graphite under an argon or co atmosphere. With graphite and temperatures of up to 1200°C, he located that iron formed initial, accompanied by an impure Cr203' At higher temperatures, the development of iron was accompanied by that relating to Fe3C and (Fe, Cr7C3), The original metallic iron was at some point transformed into Fe3C, along with the chromite spinel gradually transformed to MgA1204' A comparable reaction sequence occurred when co was used because the reductant. These results suggest Transvaal chromite is reduced through deadly carbon monoxide, an interpretation supported by microstructural evidence that the initial reduction occurred in the edges ofthe chromite particles (topochemicaI5).

Dewar and See20 conducted reducing experiments on chromite from your Wintervcld mine (Table Ill) employing chars, coke, coal, and graphite as decreasing agents in a thermogravimetric furnace. Inside the Ih tests, 35 to 45 % reduction occurred at 1500°C, whereas negligible reduction occurred at 1350°C, the reduction mechanisms becoming independent from the type of reductant uscd. The rates of reduction elevated with elevated reactivities of the decreasing agents towards co2. In the later stages of reduction, the reduction was influenced each through the above factors and also by the fixed-carbon content material with the minimizing agent.

Another sample of chromite from thc Winterveld mine (Table Ill) was subjected to a series of reduction tests at 1200 to 1500°CI9,22. Observations showed a topochemical reaction, but other mechanisms could operate over such a wide temperature range. Up to 1500°C, Urquhart believed that the decrease in this Transvaal chromitc ore occurred through a solid-state reaction with a solid reductant.

Cohen and Yalcin3 conducted experiments on a South African chromite (Table Ill) using chromium being a decreasing agent. The advantages claimed with this process are that only the iron oxide is reduced, the reduction is exothermic, and also the product is carbon-free rather than otherwise contaminated through the redttctant. Chromite and chromium (17,5 percent by mass) had been briquetted and heated to temperatures amongst 700 and 1l00°C for Ih. Total iron reduction was possible limited to temperatures above 1050° C. It was discovered the quantity of chromium reductant influences the time required to total the reduction reaction, approximately 17,five percent chromium becoming optimum; thorough mixing is necessary to preserve the chromium losses at least, the iron can be leached subsequently with sulphuric acid, along with the resulting concentrates can be used for the manufacture of chromic oxide. Low-carbon ferrochromium may also be created but, as a result with the advent with the argonoxygen decarburization (AOD) process, this product just isn't required.