A Process For Reducing Hexavalent Chromium From Solid Chromite Materials

Abstract

The main object of the present invention therefore, is to reduce the hexavalent chromium to trace levels in concentrates/fines.This and other objects of the present invention can be achieved by using an organic reductant.The organic reductant used in the present invention is a powdery compound of phenolic nature. The product is extracted from a naturally occurring forest plant. It is known as Myrobalam powder and obtained by grinding a naturally occurring forest plant nut known as Terminalia Chebula (botanical name). For the first time, an organic reductant has been used successfully in the present invention for reduction of hexavalent chromium in chromite concentrates to less than 0.01 ppm.The organic product of the present invention can be used as reducing agent for hexavalent chromium from solid chromite materials. This product is environmental friendly, cost effective and impurities (which causes damage to process equipment) free organic product and hence preferable to use in continuous production process of chromite ore materials. The same is tested in commercial scale and found effective.Thus the present invention provides a process for reducing hexavalent chromium from solid chromite materials to non-detectable traces, comprising the steps of: preparing a water solution of myrobalain powder in a tank with desirable concentration; contacting chromite material with hexavalent chromium with said solution for reducing the hexavalent chromite content; and testing samples of reduced hexavalent chromite material.

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2
FIELD OF APPLICATION
The present invention relates to a process for reducing hexavalent chromium from solid chromite materials. In particular, the invention relates to a process for reduction of hexavalent chromium to non-detectable traces using an organic reductant.
BACKGROUND OF THE INVENTION
Chromite materials (ores/concentrates) contain hexavalent chromium in ppm levels and if it exceeds 0.05 ppm it could be environmental unfriendly as per World Health Organization and US Environmental Protection Agency. The chromite ore materials will be preferred by the customers only if it is hexavalent chromium free, this is the differential for future marketing of chromite ore materials.
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Hence there was a need to address this issue. An environmental friendly, cost effective, down the line metallurgically by compatible process in terms of impurities needed to be developed using newer reductants especially with solids. This is a challenging task and is mostly possible only by using organic reductants or any other innovative method where no inorganic salts are used.
SUMMARY OF THE INVENTION
The main object of the present invention therefore, is to reduce the hexavalent chromium to trace levels in concentrates/fines.
This and other objects of the present invention can be achieved by using an organic reductant.
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The organic reductant used in the present invention is a powdery compound of phenolic nature. The product is extracted from a naturally occurring forest plant. It is known as Myrobalam powder and obtained by grinding a naturally occurring forest plant nut known as Terminalia Chebula (botanical name). For the first time, an organic reductant has been used successfully in the present invention for reduction of hexavalent chromium in chromite concentrates to less than 0.01 ppm.
The organic product of the present invention can be used as reducing agent for hexavalent chromium from solid chromite materials. This product is environmental friendly, cost effective and impurities (which causes damage to process equipment) free organic product and hence preferable to use in continuous production process of chromite ore materials. The same is tested in commercial scale and found effective.
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Thus the present invention provides a process for reducing hexavalent chromium from solid chromite materials to non-detectable traces, comprising the steps of: preparing a water solution of myrobalain powder in a tank with desirable concentration; contacting chromite material with hexavalent chromium with said solution for reducing the hexavalent chromite content; and testing samples of reduced hexavalent chromite material.
BREIF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be described in detail with the help of the figures of the accompanying drawings in which
Figure 1 shows in schematic form the setup used in the present invention for reducing the hexavalent chromium from solid chromite materials.
Figure 2 shows a graph giving reduction in hexavalent chromium against different dosage of the organic product of the present invention.
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DETAILED DESCRIPTION
Table 1 shows the approximate analysis of the organic reductant of the present invention.
Table 1
Component
Composition, %
Moisture
6.5
Volatile matter
55
Fixed carbon
21.5
Ash
17
A schematic diagram of the setup of the present invention is shown in Figure 1. The setup consists of a polyethylene tank 2, a stirrer 3 with a motor 4 which is used for making the organic reductant solution with desired concentration (w/v). The addition of the organic solution to the circuit for contacting chromium materials 1 (concentrates/ores) can be controlled with a globe valve 6 fitted in a discharge line 7 of a pump 5.
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The organic reductant solution is prepared of desired strength (w/v) by mixing given amount of organic reductant powder with a fixed volume of water. The solution is continuously stirred and pumped and brought in contact with chromite materials 1. Chromite material samples are taken before each test for initial Cr(VI) present in the chromite concentrates. Tests are conducted at given organic reductant dosages for 2 to 2.5 hours. During each test, concentrate samples are collected at regular intervals for Cr(VI) analysis.
The organic product is of phenolic nature and a powdery compound. This product is extracted from the forest plant product and used for the reduction of hexavalent chromium from solid chromite material.
Plant trials were carried out and the results obtained from plant trials with chromite materials have been discussed below.
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Table 2 shows the quantities of chromite ore material treated (column 1), the quantities of organic reductant used to treat this chromite ore material (column 2) and quantities of water used (column 3) to prepare the organic reductant solution.
Table 2
1
2
3
Chromite ore material (Kg / hr)
Organic reductant (Kg)
Solution water (Liter)
50000
20
570
Table 3
1
2
3
Flowrate of organic
Hexavalent chromium
Hexavalent chromium
reductant solution used
content (ppm) of
content (ppm) of
to treat the chromite ore
chromite ore material
chromite ore material
material (lit / min)
before treatment of
after treatment of
organic reductant.
organic reductant
9.50
0.415
0.002 (Non Detectable)
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Table 3 shows the flow rate of the prepared organic reductant solution used (column 1), the hexavalent chromium content in ppm of the chromite ore material before the treatment of organic reductant (column 2), and the hexavalent chromium content in ppm of the chromite ore material after the treatment of organic reductant (column 3).
The determination of hexavalent chromium in solid chromite ore material is carried out using the modified US-EPA standard method 7196a and Japanese method JIS K0102-1993.
The chromite material samples collected before the treatment contained Cr(VI) in the range of 0.4 to 0.6 ppm. Tests were conducted at different dosages of organic product with objective of finding the minimum quantity required of the same for the Cr(VI) reduction to traces (i.e. less than 0.01 ppm). The results obtained during the four comprehensive tests at different dosage are shown in Figure 2. The organic product quantities (dosages) used during the tests are expressed in dry basis in terms of calculated dry kg's of organic reductant used per ton of concentrate treated for one hour test in the circuit. During each test, at given dosage of organic reductant 5 / 6 representative samples of concentrate were collected for Cr(VI) analysis and the average residual Cr(VI) is indicated.
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It can be seen from Figure 2, that a minimum quantity of 0.4 kg of organic product was capable of reducing the Cr(VI) to traces in a ton of concentrate. After treatment, Cr(VI) in concentrate was reduced to traces and no detectable residual (Cr(VI) was present. At higher dosages there was no further significant effect on Cr(Vl) reduction. Hence 0.4 kg or organic reductant (dry basis) was optimized amount required for a ton of concentrate treatment.
From Figure 2 it is evident that the organic reductant reduces the hexavalent chromium in chromite ore materials to non-detectable traces.

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