Patent Description:
Ferrochrome is an essential alloy for stainless steel production. In Canada, the discovery of large chromite deposits in the Ring of Fire area in Northern Ontario has resulted in increased interests in the exploration of the deposits and its subsequent exploitation and processing to produce ferrochrome alloys.

Currently, most of the chromite ores or concentrates are processed by smelting with a reducing agent in electric arc furnaces to produce high-carbon ferrochrome or charge chrome. High-carbon ferrochrome contains typically <NUM>-<NUM> wt% of chromium, and <NUM>-<NUM> wt% of carbon, whereas charge chrome typically has chromium content of <NUM>-<NUM> wt% and carbon content of <NUM>-<NUM> wt%. These two types of ferrochrome are intermediate products primarily used for stainless steel production.

In a typical electric arc furnace smelting operation, electric current is passed through electrodes to generate heat and keep the temperatures sufficiently high to melt the feed materials and keep the slag in molten form. Endothermic reduction reactions take place by the addition of reductant to produce the molten ferrochrome alloy (Cr-Fe).

During the reduction process, MgO and Al<NUM>O<NUM> are released from chromite to the molten slag phase. Molten alloy and molten slag phases in the electric arc furnace form two separate layers due to their immiscibility and substantial density difference. Separation of the molten alloy from the molten slag is then achieved by tapping them separately. Molten ferrochrome is tapped and casted in moulds, followed by crushing of the ingots to form a saleable ferrochrome product of different size fractions. An alternative product in the form of granulates is produced by water granulation of the molten ferrochrome.

There are certain drawbacks associated with conventional electric arc furnace smelting operation.

Among the drawbacks, conventional electric arc furnace smelting technologies for ferrochrome production are highly electrical energy intensive, mainly caused by the fact that smelting at temperatures as high as <NUM> is required to keep the ferrochrome alloy and the slag phase molten during the reduction of chromite. Electrical energy consumption ranges from <NUM> to <NUM> MWh per tonne of ferrochrome produced. As a result, ferrochrome production is heavily constrained by the electrical power supply and the profitability of the smelting operation is greatly influenced by the local/regional price of electricity.

Therefore, efforts have been made to reduce the electrical energy consumption relating to conventional smelting technologies by incremental improvement, and by developing alternative processing routes for ferrochrome production.

For example, patent application <CIT> discloses a process wherein the chromite ore is reduced by reformed natural gas for reduction at sufficiently high temperatures. According to this application, fines of chromite are agglomerated with carbon and an accelerant (i.e. an alkaline compound in the form of an oxide, hydroxide or carbonate). The agglomerates, preferably in the form of pellets, are then reduced by reformed natural gas in a temperature range of <NUM> to <NUM>.

<CIT> discusses high temperature carbonaceous reduction of chromite ore with the usage of boron oxide (B<NUM>O<NUM>) or borate as a fluxing agent for the production of medium carbon ferrochrome. This application describes first making pellets from a mixture of chromite ore, coal and the above-mentioned catalyst; the pellets are then subjected to high temperatures of <NUM> or lower, resulting in partial melting of the refractory oxides initiated by the flux followed by the reduction. The iron/chromium/residual carbon mixture is then further separated from the slag. Medium carbon ferrochrome alloy is produced by further melting the mixture in a melter.

Patent application <CIT> discloses a process whereby chromite ore/concentrates are oxidized at a temperature of <NUM> to increase the reactivity of chromite, which, according to this application, is due to the formation of vacancies during the oxidation of FeO to Fe<NUM>O<NUM>. The oxidized ore/concentrates are further mixed with excess carbonaceous reductant and catalyst in the form of quartz (SiO<NUM>) and lime (CaO) before pelletization. Reduction is carried out at <NUM>-<NUM>, which supposedly would result in the formation of high-carbon ferrochrome nuggets with diameters measuring from <NUM> to <NUM>. This application claims that separation of the metal and slag phases can be achieved by physical methods and that a metallization degree of <NUM>-<NUM>% can be achieved.

Patent application <CIT> discloses a method for direct reduction of oxidized chromite ore fines composite agglomerates in a tunnel kiln to produce a reduced product that can be used in ferrochrome or charge chrome production. According to this application, prior to agglomeration, the ground run of mine chromite ore fines are first heat-treated in a tunnel kiln or a rotary kiln at temperatures up to <NUM> for a period of <NUM>-<NUM> minutes in the presence of air to allow the oxidation of FeO present in chromite spinel to form sequioxide lamellae on the surface of chromite particles. The oxidized chromite ore fines are then agglomerated with carbonaceous reductant, quartz or quartzite and lime as the slag formers and bentonite as the binder. The agglomerates are placed on the carbonaceous layer on the surface of tunnel kiln cars or trolleys, and subjected to reduction in the tunnel kiln, achieving metallization degrees of <NUM>-<NUM> wt% for Cr and <NUM>-<NUM> wt% for Fe. The reduced product or agglomerate can be used in ferrochrome or charge chrome production.

Patent <CIT> describes a process for increasing the chromium-iron ratio of the chromite ore. According to this patent, the ore fines produced from grinding chromite ores or concentrates are mixed with ground carbonaceous reducing agent of up to <NUM> wt%, water, and a binding agent (e.g. sodium chloride, calcium chloride, sodium carbonate, or starch) before forming pellets. The proportion of the reducing agent is important so as to allow only reduction of the iron content while avoiding reduction of the chrome content. Partial reduction takes place by subjecting the pellets to a temperature of <NUM>-<NUM> for about <NUM> minutes. The reduced iron can subsequently be removed by leaching the roasted pellets with acid, producing the leached pellets having higher chromium to iron ratio than the original chromite ore or concentrate.

<CIT> discloses a pyrometallurgical reductive process characterised in that firstly pellets comprising a mixture of ore and coke precursor are heated in the absence of air so that the coke precursor is converted to coke and secondly the so formed pellets are treated in a subsequent reductive step to obtain as product discrete pellets comprising reduced ore set in a matrix of coke. Preferably the matrix of coke is in the form of an external coating to the pellet.

Notwithstanding the above improvements on conventional smelting technologies, there remains the need for effective and energy-efficient processes for the reduction of chromite to produce ferrochrome alloys.

The present invention discloses a novel process for the production of ferrochrome.

According to the present invention, the reduction of chromite takes place at much lower temperatures (e.g. <NUM> to <NUM>) than the current state of art, wherein the ferrochrome and unwanted residue produced are in their solid forms. Calcium chloride (CaCl<NUM>) is added as a catalyst to accelerate the solid reduction and enhance particle growth of the metallic phase (i.e. ferrochrome) during reduction.

The catalyst calcium chloride (CaCl<NUM>•xH<NUM>O) can be in the form of anhydrous (x=<NUM>), hydrated (<NUM><x≤<NUM>), or aqueous solution, depending on its water content.

Other features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings, which illustrate, by way of example, the principles of the invention.

The present invention addresses direct reduction of chromite using calcium chloride as catalyst for the production of ferrochrome alloy.

<FIG> includes flowcharts of two commercial smelting processes for ferrochrome production (i.e. Outotec and Premus ferrochrome processes), whereas <FIG> is a flowchart showing a direct reduction process for the production of ferrochrome from chromite ore/concentrate as disclosed according to the present invention.

As shown in <FIG>, calcium chloride (CaCl<NUM>) is added as a catalyst to accelerate the solid reduction and enhance the particle growth of the metallic phase (i.e. ferrochrome) during reduction. The reduction of chromite takes place at much lower temperatures (e.g. <NUM> to <NUM>) compared to the conventional smelting technologies, and the ferrochrome and unwanted residue produced are in their solid forms.

More specifically, the direct reduction process disclosed herein comprises the following steps:.

After milling, chromite ores or concentrates in their powder form are first mixed with no less than the stoichiometric amount of carbonaceous reductant (e.g. graphite, coke, coal, or char, etc.), and CaCl<NUM>. Stoichiometric amount of reductant is defined as the amount of carbon in the reductant required to reach complete reduction of chromium and iron oxides from the chromite ore/concentrate, forming carbon monoxide as the gaseous product, with the extra carbon required to form alloy in its carbide form, particularly (Cr,Fe)<NUM>C<NUM>.

Calcium chloride is in the form of anhydrous, hydrated, aqueous solution, or any combination thereof, with the total mass of the catalyst (i.e. anhydrous CaCl<NUM>) in the range of <NUM>-<NUM> wt% (dry weight) of the chromite ore/concentrate.

When calcium chloride is in solid form, it is preferable that calcium chloride is in fine ground powder form to ensure homogeneity during mixing with chromite and the carbonaceous reductant.

Control of particle sizes for both the chromite ore or concentrate and the reductant affects the kinetics of reduction and the particle sizes of the final ferrochrome alloy product.

The particle size of the chromite ore or concentrate is less than <NUM> mesh (Tyler) as larger particle sizes will require longer retention times for reduction.

Reductant with particle size fraction passing <NUM> mesh is used.

A person skilled in the art would appreciate that the amounts of carbonaceous reductant and CaCl<NUM> can be optimized for specific types of chromite ore/concentrate for improved metal recovery, lower amounts of reductant, and/or shorter retention times.

To allow for easier handling of the powder feed while minimizing the dust generation during handling and subsequent processing, the mixture of chromite, reductant, and CaCl<NUM> is preferably agglomerated by pelletizing (e.g. disc or drum pelletizer) or briquetting to form pellets or briquettes for reduction.

The catalyst calcium chloride in the mixture tends to absorb moisture during mixing and pelletizing/briquetting, which acts as a binder and facilitates the pelletizing/briquetting process.

The agglomeration step is optional and does not exclude the feasibility of directly processing the mixture of chromite, carbonaceous reductant, and CaCl<NUM> without the agglomeration step, as indicated by the dashed line in <FIG>.

The feed material to the drying process may be the green pellets/briquettes produced from the agglomeration step, or the mixtures produced from the mixing step in the case where agglomeration is not used.

The feed material is dried at temperatures high enough <NUM> - <NUM>° C to remove moisture before direct reduction.

Preferably, the direct reduction of the feed is performed in a shaft furnace, a multi hearth furnace, a tunnel kiln, a rotary kiln, or the alike, heated by burning fuels (e.g. coal, natural gas, etc.), thus eliminating the need for electric energy. This however, does not exclude the use of an electrically heated furnace for reduction.

During operation, temperature of the feed is controlled, in the <NUM> to <NUM> range. A person skilled in the art would appreciate that temperatures higher than <NUM> will result in a faster reduction rate, and shorter retention time for complete reduction, but at the cost of consuming more energy. Higher temperature could also potentially cause substantial evaporation of CaCl<NUM>, which could be entrained in the off-gas, or deposited onto the cooler region of the furnace chamber.

The time required for near-complete reduction is generally less than <NUM> hours, but depends upon factors such as temperature, and the particle sizes of chromite and reductant.

The off-gas from the direct reduction process is rich in CO, which is then processed by scrubbers and subsequently stored or combusted for heat recovery. For example, the heat generated from CO combustion is further used for drying and preheating the feed before direct reduction, thereby further reducing the energy consumption. The CO-rich off-gas could also be used for generating electricity.

<FIG> further illustrates schematically the role of CaCl<NUM> in the reduction process where steps (a) to (g) represent the following:.

Describing the process in more detail, catalyst CaCl<NUM> in the feed melts when the temperature is above approximately <NUM>, and creates a liquid media to enable incongruent dissolution of chromite and transport of reducible ions (e.g. Fe<NUM>+, Fe<NUM>+, Cr<NUM>+) from chromite to carbonaceous reductant particles where metallization takes place. Transport of the Cr and Fe species can also occur in the gas phase as ionic species. Metallization starts with the nucleation and growth of the metallic phase on the carbonaceous reductant particles. The gaseous product from the direct reduction (i.e. CO) escapes or is released through pores of the feed. Due to the closely packed nature of the particles in the feed, adjacent ferrochrome particles coalesce. This facilitates the growth of ferrochrome particles and the subsequent separation of ferrochrome particles from the unwanted gangue and spinel materials.

The solid product from direct reduction is processed, for example, it is quenched in water, and leached for the recovery of CaCl<NUM> by taking advantage of the highly water-soluble nature of CaCl<NUM>. The product disintegrates during leaching due to the thermal shock occurred during quenching, and during the removal and dissolution of CaCl<NUM> by leaching.

CaCl<NUM> recovered from the leaching process will be re-used. Because CaCl<NUM> does not participate in the reduction reactions in the high temperature direct reduction process, it will be mostly recovered and recycled, thus minimizing the material costs. The recovery of CaCl<NUM> by water leaching is around <NUM> by wt%.

The CaCl<NUM> catalyst is re-generated through precipitation from the leachate, and subsequently recycled for mixing with chromite ore/concentrate and reductant. This is performed by heating/boiling to supersaturate the solution with respect to CaCl<NUM> through evaporation.

The heat required may be produced by burning fuels or the CO-rich off-gas produced from the direct reduction process. For example, the amount of heat generated from burning the CO-rich off-gas is sufficient for the complete precipitation of CaCl<NUM> from leachate based on thermal balance calculations.

An alternative to precipitation is to produce concentrated CaCl<NUM> solution by boiling off excess water from the leachate. The concentrated CaCl<NUM> solution is then recycled and sprayed and mixed with the chromite ore/concentrate and reductant.

This re-generation of CaCl<NUM> substantially minimizes the overall consumption of CaCl<NUM> per tonne of ferrochrome produced.

To enable sufficient liberation of the ferrochrome alloy particles following leaching by water, mild crushing may be required.

Subsequent separation of ferrochrome alloy from the residual gangue and refractory spinel particles is possible considering the following factors:.

A nested combination of these techniques may be utilized to make the physical separation more efficient.

The process as described above for the direct reduction of chromite for ferrochrome production differs from the conventional processes and provides, inter alia, the following advantages:.

Examples <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> do not fall within the scope of the claims.

High temperature reduction tests were conducted using a vertical electrical tube furnace. For each test, the sample was loaded in an alumina crucible and then placed inside the sealed alumina tube of the electric furnace. During heating, the chamber of alumina tube was continuously purged with a controlled flow of Ar to maintain an inert atmosphere. Off-gas was analyzed continuously with a gas analyzer for its CO and COz concentrations. The results from the off-gas analysis were recorded by a data acquisition system.

Products from the furnace reduction tests were subjected to characterization, such as optical microscopy, scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), and X-ray powder diffraction (XRD).

Degrees of metallization for both Fe and Cr were assessed by an acid selective catalyst leaching method accepted and used by industrial smelters as well as researchers in the same field. Using this method, the metallic phases that formed in the products are dissolved selectively by the acid, leaving behind the oxides in the solid residue. Solid residue was further completely dissolved into an aqueous solution using Na<NUM>O<NUM> fusion technique. Solutions from both leaching and fusion were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) for their chemical composition to determine the degree of metallization.

Recovery of CaCl<NUM> from the products by water leaching is an important aspect of the proposed direct reduction process. This was performed by leaching with boiling water for <NUM> minutes. The degree of CaCl<NUM> recovery is calculated from the CaCl<NUM> contents of the leachate and residue.

After water leaching, some of the products were subjected to magnetic separation using the Frantz magnetic separator. The magnetic and non-magnetic parts were analyzed by SEM/EDS to assess the separation performance.

As a control experiment, no CaCl<NUM> was added to the sample in this test. The chemical composition of the chromite concentrate used in this example is shown in Table <NUM> below.

Chromite concentrate having the size range of <NUM>∼<NUM> mesh was firstly mixed thoroughly with <NUM> wt% graphite powders (<NUM>∼<NUM> mesh) before pelletization. Pelletized samples were heated in an inert argon atmosphere at <NUM> for two hours as shown in <FIG>. Reduction of the chromite by graphite took place resulting in the formation of CO and CO<NUM> as the gaseous product.

In <FIG>, concentrations of CO and CO<NUM> in the off-gas reflect the rate of reduction. Reduction reactions started to take place at approximately <NUM>, resulting in the formation of CO<NUM>. Higher temperature resulted in the evolution of CO as the main gaseous product, reaching a peak of about <NUM> vol%. At the end of the two-hour dwelling at <NUM>, there was still approximately <NUM> vol% CO evolution, an indication that the reduction was still far from reaching completion. This was confirmed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses on the sample product.

In contrast to the control test, per <NUM> of chromite concentrate, <NUM> of graphite powder having a size range of <NUM>∼<NUM> mesh and <NUM> of finely ground CaCl<NUM> was added and mixed before pelletization. The green pellets were heated in an inert atmosphere at <NUM> for <NUM> hours before cooling down.

Compared to the control test of Example <NUM>, much higher evolution of CO took place in Example <NUM>. As shown in <FIG>, the CO peak reached as high as <NUM> vol%, evidence that much accelerated reduction reactions took place due to the presence of CaCl<NUM>.

The reduced pellets were subjected to further characterization. Based on the examination of the reduced product, metallization degrees of <NUM> wt% Cr and <NUM> wt% Fe were achieved during direct reduction.

<FIG> is a photomicrograph of the cross section of the reduced pellets taken by SEM, showing the particle size and morphologies of the ferrochrome alloy (white) and the residual refractory spinel (grey) particles formed during reduction. SEM observations indicate partial sintering of adjacent alloy particles. This sintering and growth of alloy particles facilitate physical separation of ferrochrome from the unwanted materials. The porous grey particles were composed mainly of spinel (MgAl<NUM>O<NUM>) and forsterite (Mg<NUM>SiO<NUM>) that are devoid of alloy particles as micro inclusions. This feature ensures maximum separation of ferrochrome alloy from unwanted materials without the need of further grinding.

Water-leach tests were performed on the reduced pellets, resulting in a recovery of <NUM> wt% CaCl<NUM> into the leachate, showing the feasibility of recovering the CaCl<NUM> for reuse, thus further lowering the material cost.

The reduced product after water-leach was subjected to a single-stage magnetic separation. <FIG> shows the morphologies of the magnetic (left) and non-magnetic (right) fractions of the product following magnetic separation. As illustrated, a significant proportion of the gangue particles reported to the non-magnetic fraction, evidence of the feasibility and the effectiveness of the magnetic separation. Recovery of the ferrochrome is increased by multi-stage magnetic separation or by combining with other separation methods.

Charcoal having particle sizes in the range of <NUM>-<NUM> mesh was used as the carbonaceous reductant in this example. Chromite concentrate of <NUM>-<NUM> mesh was mixed with <NUM> wt% charcoal and <NUM> wt% CaCl<NUM> before pelletization. The green pellets were subjected to drying at <NUM> for one hour followed by heating at <NUM> for two hours in the furnace before cooling to room temperature.

Subsequently, the reduced pellets were leached with water for the recovery of CaCl<NUM>. During leaching, the pellets collapsed to powders partially due to the removal of CaCl<NUM> by dissolution, and by crushing them gently.

<FIG> shows the surface morphology of the dried powders after water leaching. Relatively clean ferrochrome alloy particles are observed, evidence that a near-complete liberation of the ferrochrome alloy particles from the reduced chromite and other unwanted particles. Because the charcoal used in this example was porous, the ferrochrome alloy particles formed were also porous resulting from the distinct reduction mechanism as discussed previously and shown in <FIG>, step d.

A multi-step magnetic separation test using various magnetic intensities was performed on the dried powders. <FIG> shows the magnetic and non-magnetic products from one magnetic separation test. The magnetic portion (left) is composed of ferrochrome alloy particles with very few slag and/or residual chromite/spinel inclusions. Residual spinel particles with very low contents of Cr and Fe along with other unwanted components form the non-magnetic portion (right).

Chromite concentrate having particle sizes in the <NUM> to about <NUM> mesh range was first mixed with <NUM> wt% flake-shaped graphite (<NUM>-<NUM> mesh) and <NUM> wt% ground CaCl<NUM> powder. The mixture was subjected to pelletization to form green pellets. The green pellets were heated at <NUM> to reduce its water content before heating at <NUM> for two hours in an inert atmosphere for direct reduction.

After the reduced pellets cooled down to room temperature, a reduced pellet was sectioned to prepare a polished section for characterization using SEM.

<FIG> shows the cross section of the reduced pellet. The white particles are ferrochrome alloy particles, and the grey particles are the residual chromite/spinel particles with CaCl<NUM>. The residual chromite/spinel particles have an average Cr concentration of about <NUM> wt%, evidence of a high degree of reduction. Most of the ferrochrome particles are not physically associated with the residual chromite/spinel and slag particles, evidence of a high degree of liberation.

The reduced pellets were leached with water to recover CaCl<NUM>. The pellets disintegrated during leaching and by mild crushing in water. Grinding was not necessary and should be avoided to minimize the formation of extra fine particles.

Because the particle size of graphite was larger than that of chromite in the green pellets, a preliminary separation of the ferrochrome particles from the gangue materials was performed by wet-sieving to reject a significant portion of the unwanted material.

<FIG> illustrates the oversize and the undersize products from the wet-sieving process using <NUM> mesh sieve. The undersize particles are mainly unwanted materials, evidence of the effectiveness of the wet-sieving technique to reject the unwanted materials. The unwanted material in the oversize fraction formed during direct reduction when local sintering took place among adjacent chromite particles, resulting in an increase of the residual chromite particle size. The presence of siliceous gangue in the chromite ore/concentrate was likely the cause of local sintering. Thus, separation by wet-sieving would be more effective when dealing with chromite ores/concentrates having lower contents of the siliceous gangue in the feed.

Magnetic separation was performed on the oversize product. <FIG> shows the magnetic fraction which is the ferrochrome product and the non-magnetic fraction from magnetic separation, evidence of the feasibility to achieve a high degree of separation of the ferrochrome product from the unwanted materials.

Chromite concentrate (<NUM>∼<NUM> mesh) was mixed with <NUM> wt% flake-shaped graphite powders (<NUM>∼<NUM> mesh) and <NUM> wt% CaCl<NUM> powders. A briquette measuring a thickness of about <NUM> was made by mixing the powder mixture with water followed by drying in an oven at <NUM>. The briquette was subjected to heating at <NUM> for two hours in an inert atmosphere before cooling down to room temperature.

<FIG> shows the cross section of the reduced briquette (left) and the surface morphology of the powders produced from water leaching of the reduced briquette (right). The residual chromite/spinel particles (grey) have an average Cr concentration of less than <NUM> wt%, evidence of high degree of reduction has taken place during the direct reduction. Very few ferrochrome alloy particles (white) are physically associated with the residual gangue and spinel particles, which means that grinding would not be needed before the separation process.

A multi-step magnetic separation test using various magnetic intensities was performed on the dried powders. <FIG> shows the magnetic and non-magnetic fractions from one magnetic separation test. The magnetic fraction (left) is composed of ferrochrome alloy particles with a few residual gangue and spinel inclusions. The residual chromite particles with low content of Cr and Fe along with other unwanted materials form the non-magnetic fraction (right).

Chromite concentrate (<NUM>∼<NUM> mesh) was mixed with <NUM> wt% graphite (<NUM>-<NUM> mesh) and <NUM> wt% CaCl<NUM> powders. Without agglomeration, the powder mixture was directly charged into the furnace for drying and reduction. Drying took place at <NUM> for one hour. Subsequently, the mixture was further heated at <NUM> for two hours before cooling down to room temperature.

After water leaching, the reduced product was wet-sieved using a sieve of <NUM> mesh. <FIG> illustrates the oversize (left) and the undersize (right) fractions, evidence of the effectiveness of wet-sieving for rejecting the unwanted particles as the undersize portion. Further physical separation is performed on the oversize fraction using other separation techniques (e.g. magnetic separation). SEM analysis shows that there is, on average, <NUM> wt% Cr in the residual chromite particles, evidence of a high degree of reduction.

Magnetic separation was further performed on the oversize product. <FIG> shows the magnetic ferrochrome product (left) and the unwanted particles in the non-magnetic fraction (right) produced from magnetic separation, evidence of the feasibility of achieving a high degree of separation of the ferrochrome product from the unwanted materials.

Chromite concentrate of <NUM>∼<NUM> mesh was mixed with <NUM> wt% graphite powder (<NUM>-<NUM> mesh), and <NUM> wt% CaCl<NUM> without pelletization. Sample powder mixture was heated at <NUM> for two hours (<FIG>).

When compared with Example <NUM>, the reduction rate was also much higher due to the presence of CaCl<NUM> even without pelletization, as can be seen from <FIG>.

<NUM> wt% of CaCl<NUM> in the product was recovered by water leaching. From the analysis by selective acid leaching, metallization degrees of <NUM> wt% Cr and <NUM> wt% Fe were achieved, evidence of complete reduction within a period of two hours at <NUM>.

Chromite concentrate of passing <NUM> mesh (<<NUM> pm) was mixed with <NUM> wt% graphite powders (<NUM>∼<NUM> mesh) and <NUM> wt% CaCl<NUM> without making pellets. Sample mixture was subjected to <NUM> for two hours. As can be seen from <FIG>, the reduction rate was relatively high.

The concentration of CO in the off-gas decreased to about <NUM> vol% before cooling down, evidence of a near complete reduction. Metallization degrees of <NUM> wt% Cr and <NUM> wt% Fe were achieved. <NUM> wt% CaCl<NUM> was recovered based on water leaching test.

Sample product was analyzed by SEM which suggests that the particle size of the ferrochrome alloy particles can be greatly influenced by the starting graphite particle size.

Chromite concentrate of <NUM>∼<NUM> mesh was mixed thoroughly with <NUM> wt% graphite powder (<NUM>-<NUM> mesh) and <NUM> wt% CaCl<NUM> before pelletization. Sample pellets were heated at <NUM> for two hours.

Concentrations of CO and CO<NUM> in the off-gas were plotted in <FIG> along with the temperature profile, as a function of time. The results for the off gas analysis after <NUM> was not shown here due to abnormalities that took place in the off gas measurement. In terms of the experimental conditions, the only difference between Example <NUM> and Example <NUM> is that sample mixture was pelletized in Example <NUM>.

By comparing their results from the off-gas analysis, the CO peak reached a much higher concentration at about <NUM> vol% for the reduction test on pelletized samples (<FIG>), meaning pelletization is beneficial in terms of further accelerating the reduction.

High metallization degrees of <NUM> wt% Cr and <NUM> wt% Fe were achieved in this test. <NUM> wt% of CaCl<NUM> was recovered based on water leaching test.

Chromite concentrate of <NUM>∼<NUM> mesh was mixed with <NUM> wt% graphite powder (<NUM>∼<NUM> mesh) and <NUM> wt% CaCl<NUM> before pelletization. Sample pellets were heated at <NUM> for two hours.

The results from off-gas analysis along with the temperature profile are shown in <FIG>. Based on the CO concentration, the reduction took place at a relatively fast rate because of the addition of CaCl<NUM> when compared with Example <NUM> control test, confirming the effectiveness of CaCl<NUM> in accelerating the direct reduction of chromite.

Metallization degrees of <NUM> wt% Cr and <NUM> wt% Fe were achieved, which were relatively low compared with other tests with CaCl<NUM> addition. <NUM> wt% of CaCl<NUM> is recovered by water leaching.

Claim 1:
A process for production of a ferrochrome alloy from a chromite ore or a chromite concentrate, comprising:
(a) mixing the chromite ore or the chromite concentrate with a carbonaceous reductant and calcium chloride to produce a feed material, wherein carbonaceous reductant with particle size fraction passing <NUM> Tyler mesh is used, wherein the chromite ore or the chromite concentrate is in powder form, wherein the calcium chloride is in the form of anhydrous, hydrated, or a combination thereof and in fine ground powder form, wherein particle size of the chromite ore or chromite concentrate is less than <NUM> Tyler mesh, wherein the chromite ore or the chromite concentrate is mixed with no less than a stoichiometric amount of the carbonaceous reductant, wherein the total mass of the calcium chloride is in the range of <NUM>-<NUM> wt% of the chromite ore or the chromite concentrate;
(b) drying said feed material at a temperature of <NUM>-<NUM> to remove moisture;
(c) feeding the dried feed material into a reaction vessel at elevated temperatures in the range of <NUM> to <NUM> for direct reduction of the chromite ore or the chromite concentrate in the dried feed material to produce a product mixture comprising an off-gas which comprises carbon monoxide and a solid product; and
(d) processing the product mixture to separate the ferrochrome alloy from residual gangue and spinel, wherein the stoichiometric amount of the carbonaceous reductant is the amount of carbon in the carbonaceous reductant required to complete reduction of chromium and iron oxides from the chromite ore or the chromite concentrate to form carbon monoxide, with extra carbon required to form alloy in its carbide form.