Title of Invention

"A NOVEL PROCESS FOR DISOLUTION OF MANGANESE DIOXIDE"

Abstract

Disclosed herein is a method of obtaining an aqueous solution manganese, iron, Cu, Co, and Ni from an insoluble metal oxide such as manganese dioxide, Fe (III) oxide, Co (III) oxide or Ni (III) oxide, comprising the steps of leaching the complex mineral oxide at about atmospheric pressure in the presence of a reducing agent selected from L ascorbic acid, pyruvic acid, oxaUc acid, salicyhc acid or an equivalent thereof, with or without a buffering agent such as herein described at room temperature followed by neutralization using an alkali or ammonia for separating the metal ions leached out in solution.

Full Text

This invention relates to a chemical process for obtaining an aqueous solution of a metal compound from an insoluble solution containing the metal oxides like Mn (IV) oxide, Fe (III) oxide, Co (III) oxide, Ni (HI) oxides etc. and in particular it relates to a process of obtaining manganese compound from an insoluble oxide of manganese, i.e. dissolution of manganese oxides, and more particularly to a process of leaching of manganese dioxide ores aided by L -ascorbic acid. Present state of the art: Manganese often occurs naturally in the tetravalent oxidation state for example in the mineral pyrolusite (MnO.sub.2) or in ferromanganese nodules found on the floors of the Atlantic, Pacific or Indian Oceans. The nodules contain a high percentage of MnO.sub.2 but are important for their more valuable non-ferrous metal content such as copper, nickel and cobalt, which are intimately associated with the manganese dioxide phase Although high-grade ore deposits supply the bulk of the manganese for metallurgical applications, some manganese is extracted in non-elemental form from naturally occurring deposits in order to produce a high purity reactive oxide product or to up-grade low-grade ore deposits. Most of the existing processes for purifying manganese ores are purely hydrometallurgical in nature. Manganese is soluble only in divalent state. Therefore all the tetravalent manganese compounds such as MnO.sub.2 must be reduced to the divalent state before manganese can be extracted hydrometallurgically. At present this is done by a costly pyrometallurgical process, which involves the application of reducing agents such as coal, carbon, natural gas and hydrogen at a high temperature of 700° to 800*^0. The reduced ore is carefiiUy cooled to avoid re-oxidation and leached with various acid or alkaline solutions. Alternative processes have been proposed to reduce tetravalent manganese to the soluble form by an aqueous reduction process. In US patent no. 4,645,650, Fray, et al described a method of reductive dissolution of manganese by treatment with hot mineral acid such as hydrochloric acid in presence of a reductant such as coal. They have used a mineral acid like hydrochloric acid of concentration IN at a temperature of 90oC. in presence of at least half part of mass of carbonaceous material such as a naturally occurring hydrocarbon or oil or a solid organic mineral such as coal. In that method they used maximum of lOOg. of solid per liter of acid. Another chemical method described by Allen, et al in US patent no. 4,872,909 embodies addition of manganese ores to an aqueous of acid and H.sub.20.sub.2 to form a leach pulp. Brooks et al in US patent no. 4,481,040 has given a process to dissolve manganese dioxide as a part of their process to dissolve chromium containing oxide deposits. At a temperature of 95°C they used reducing agent oxalic acid in nitric acid solution to dissolve Mn0.sub.2.Manganese dioxide destruction took between 0.5 to 1 hours. Ammoniacal ammonium chloride solution containing glucose has been proposed for reducing manganese and has the advantage of iron not dissolved. Limitations: A. Existing pyrometallurgical process using reducing agents as coal, carbon etc. has got the limitations as stated below. a. High thermal energy cost. b- Polluting effluent gases. c. Not applicable in case of high moisture containing ferromanganese nodules due to high preheating cost involved. B. Hydrometallurgical processes developed so far also have their own limitations as: a. Use of high temperature entailing thermal energy cost, b. Long reaction time. c. Corrosiveness of concentrated acidic or alkaline reagents. d. Costly reducing agents as sugars or hydrogen peroxide. e. Polluting and hazardous gaseous as well as liquid effluents. f Large proportion of acid consumption in case of hydrochloric acid to form chlorine by product, g. High alkali demand for subsequent neutralization steps. Proposed solution (with examples): In this invention, the oxidation state of the metal in the insoluble oxide is higher than in the solution. The invention will be described as it applies to manganese, whose insoluble oxide is MnO.sub.2 and soluble metal values are Mn (II). It is an object of the present invention is the provision of an improved process for leaching of metal oxide ores such as manganese, iron, cobalt or nickel and especially, manganese oxide ores. Another object of the present invention is to provide a dissolution process for oxides that proceeds much more rapidly than other conventional processes. 95% MnO.sub.2 dissolution can be achieved within minutes at room temperature. A further object of the present invention is the provision of a process where no heating of the oxide or leach pulp is required saving a lot of energy cost. Still another object of the present invention is to provide a process where the products oi the reactions are innocuous. No polluting gaseous bye products are evolved in the process. A still another object of the present invention is the provision of a process where the enclosure of the leaching vessel is not required One more object of the present invention is to provide a process where due to low acidity of the leaching reagent appUed, the alkali or ammonia demand for the subsequent neutralization step (for separation of metal ions leached out in solution) will be much smaller compared to that required in conventional minerd acid leaching process. Yet another object of the present invention is the provision of a process where the solutions used and produced are mild orgmiic acids requiring no corrosion-resistant materials of construction. By the use mild organic acids, material demands on the leaching vessels are much less severe than those required for the mineral acids used in prior art processes requiring use of elevated temperature and pressure. The much shorter interaction time and low acidity permit use of stainless steel vessels while titanium or other exotic alloys are required to withstand corrosion in leaching with mineral acids. In addition since the leaching takes place at ambient temperature and pressure, ^ass vessels or glass -lined vessels can also be used. According to the present invention, there is provided a method of obtaining an aqueous solution of metal compound/values from an insoluble metal oxide, the metal having a lower oxidation number in the solution than in the insoluble state, comprises treating the insoluble metal oxide at about atmospheric pressure in the presence of a reducing agent with or without a bufifering agent at room temperature. The amount of reducing agent can be at least 1:2 molar ratio of metal oxide: reducing agent. The reducing agent used is selected from a whole rsuige of organic reducing agents such as ascorbic acid, pyruvic acid, oxalic acid, salicylic acid etc. The buffering agent is selected from a range of reagents applicable to a pH range of 3 to 4, such as sodium hydrogen pthalate, perchloric acid, sodium bicarbonate, sodium acetate etc. In case, ther This process may also find another application in purification of the metal. The invention is a hydrometallurgical treatment for extracting metal values such as manganese, iron^ cobalt or nickel, and especially manganese fi-om the oxide ores. These and other attributes of the invention will become clearer upon a thorough study of the following description of the best mode carrying out the invention, particularly when reviewed in conjunction with the examples. To eliminate spurious effects, the method was performed on chemical-grade manganese dioxide MnO.sub.2. In some trials the method was however shown to work on manganese nodules. In the nodules trials, the dissolution of MnO.sub.2 was accompanied by dissolution of other valuable non-ferrous metals such as copper, nickel and cobalt. The theory of the invention involves use of L-ascorbic acid as a reducing agent to render manganese dioxide soluble in aqueous solution. The reaction is 2Mn0.sub 2 + H2A -» 2Mn(II) + A + H sub.2 O where A is dehydroascorbic acid. The preferred temperature of reaction is room temperature. The rate of reaction is almost independent on molar ratios of oxide and ascorbic acid above 1:2 ratio of manganese oxide: ascorbic acid. Molar ratios manganese dioxide: ascorbic acid was tried of 1:2, 1:3, 1:4 and 1:5. The manganese dissolution did not improve further after the first one. The concentration of solids, that is MnO.sub.2 in the ascorbic acid solution were experimentally varied from 10 g/1 to 100 g/l. The extent of manganese dissolution as well as reaction rate was found to be independent of concentration as long as molar ratio of oxide: ascorbic acid was varied accordingly. The temperature has no significant role to play in the reaction since at room temperature considerable manganese dissolution was achieved. While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing fi^om the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Following these trials the suitable methods according to the invention are as follows: Example I 100 ml 0.3 M aqueous solution of L ascorbic acid (that is, 52.8g/l) was prepared and stirred throughout. To it was added 8.8 g/1 of manganese dioxide MnO.sub.2 (that is, 0.1 M). The solution was stirred for ten minutes. The concentration of divalent manganese Mn (II) ions in the solution rose immediately. After 10 minutes the resultant solution was filtered using 45micron Millipore filter paper. After proper washings the residue collected was dried and weighed to determine un-dissolved manganese dioxide remaining in the liquor if any. That helped to determine dissolved Mn (II) gravimetrically. The filtrate with the wash water was analyzed for Mn (II) with aid of inductively coupled plasma spectro-photometry (ICP) method. Both the analytical methods confirmed around 95% Mn dissolution in the process. The pH and Eh with respect to saturated calomel electrode was measured both at the start and end of the experiment. All these data are shown in Table 1. As can be observed fi"om Tablet an increase in pH of the leach liquor confirming consumption of H. super. + ion and a decrease in Eh showing the reducing atmosphere lays credence to our method of rapid reduction of the oxide. For the sake of comparison manganese dioxide dissolution test was carried out in highly concentrated hydrochloric acid solution for the same time period. 100 ml UN solution of hydrochloric acid (that is, 1:1 HCl) was prepared. To it was added 8.7g/l of manganese dioxide MnO.sub.2 and the solution was stirred for ten minutes. After proper washings the residue collected was dried and weighed to determine un-dissolved manganese dioxide remaining in the liquor. That helped to determine dissolved Mn (II) gravimetrically. The filtrate with the wash water was analyzed for Mn (II) with aid of Inductively coupled plasma (ICP) spectrophotometry method. Both gravimetric and spectrophotometry confirmed that, only 30% of manganese dioxide dissolved under that extreme condition, which is far lower compared to the dissolution obtained in our process. Example2: In a slight variation of the process, as described in Examplel, 100 ml 0.1 M aqueous solution of L ascorbic acid (that is, 17.6 g/1) was prepared and stirred throughout. To it were added 7g/l of manganese dioxide MnO.sub.2 (O.IM) and 204.23g/l sodium hydrogen pthalate (that is, O.IM concentration) as buffering agent. The solution was stirred for ten minutes with the help of a magnetic stirrer. The concentration of the divalent manganese Mn (II) in the solution rose immediately. After proper washings the residue collected was dried and weighed to determine undissolved manganese dioxide remaining in the liquor if any. That helped to determine dissolved Mn (II) gravimetrically. The filtrate with the wash water was analyzed for Mn (11) with aid of Inductively coupled plasma spectrophotometry method. Both the analytical methods confirmed around 95% Mn dissolution in the process. The pH and Eh with respect to saturated calomel electrode was measured both at the start and end of the experiment. Al these data are shown in Tablel. As can be observed fi^om Tablel, an increase in pH of the leach Uquor confirming consumption of H.super, + ion and a decrease in Eh showing the reducing atmosphere confirms our method of rapid reduction of the oxide. References: U. S. Pat. No. Year Inventor (/s) 4,645,650 February, 1987 Fray, et al. 4,872,909 October, 1989 Allen, et al. 4,481,040 November, 1984 Brookes, et al. We claim: L A method of obtaining an aqueous solution of a metal compound from an insoluble metal oxide, the metal having a lower oxidation number in the solution than in the insoluble oxide, comprising treating the metal oxide at about atmospheric pressure, in the presence of a reducing agent, and with or without a buffering agent at room temperature. 2. A method according to claim 1, wherein the metal compound is manganese, iron, cobalt or nickel and the insoluble metal oxide is manganese dioxide, Fe (III) oxide, Co (HI) oxide, or Ni (III) oxide, 3. A method according to claim 2, wherein the insoluble manganese dioxide is a complex mineral like ocean nodule which contains minor metals such as Cu, Co and Ni that remain occluded in this phase. 4. A method according to any one of claims 1 to 3, wherein separation of the leach pulp into a solid fraction and a liquid fraction containing mostly Manganese, copper, luckel and cobalt in solution is carried out by filtration. 5. A method according to any one of claims 1 to 4, wherein the reducing agent is organic in nature and the buffering agent is selected from a range of reagents that are applicable to a pH range of 3 to 4. 6. A method according to claim 5, wherein the organic reducing agent is L ascorbic acid, pyruvic acid, oxalic acid, salicylic acid or an equivalent thereof, and the buffering agent is selected from sodium hydrogen pthalate, perchloric acid, sodium bicarbonate, sodium acetate or an equivalent thereof 7. A method according to claim 6, wherein the molar ratio of the reducing agent is at least 2:1 with respect to oxide. 8. A method according to claim 6 or 7, wherein the reducing agent is L ascorbic acid. 9. A method according to any one of claims 1 to 8, wherein sodium hydrogen pthalate is used as a buffering agent. 10- A method according to claim 9, wherein the molar ratio of sodium hydrogen pthalate to manganese dioxide is 1:1. 11. A method according to claim any one of claims 1 to 10, wherein the reaction time is only ten minutes. 12. A method according to any one of claims 1 to 8 and 11, wherein the reaction is carried out without the buffering agent and in the presence of a highly concentrated reducing agent. 13. A method according to claim 11, wherein the concentration of the reducing agent is three times higher than the one used in the presence of the buffering agent. 14. A method of obtaining an agueous solution of a metal compound from an insoluable metal oxide, substantially as hereinbefore described and illustrated in the examples.

Documents:

027-che-2003-abstract.pdf

027-che-2003-claims duplicate.pdf

027-che-2003-claims original.pdf

027-che-2003-correspondnece-others.pdf

027-che-2003-correspondnece-po.pdf

027-che-2003-description(complete) duplicate.pdf

027-che-2003-description(complete) original.pdf

027-che-2003-form 1.pdf

027-che-2003-form 19.pdf

027-che-2003-form 26.pdf