|Title of Invention||
AN IMPROVED METHOD OF OBTAINING AN AQUEOUS SOLUTION OF METAL COMPOUNDS
|Abstract||Disclosed herein is an improved method of obtaining an aqueous solution of metal compounds from a mixture of insoluble metal oxides and in particular a process of leaching of ocean manganese nodules to bring valuable metals like copper, cobalt and nickel in solution. 95% Co, 85% Cu and 93% Ni are dissolved within five minutes at room temperature.|
This invention relates to an improvement in or modification of Indian Patent Application No. 27/Mas/2003 filed on 13**^ January, 2003, wherein a chemical method of obtaining an aqueous solution of a metal compound from an insoluble solution containing the metal oxides like Mn (IV) oxide, and others.
The present invention describes a chemical method of obtaining an aqueous solution of metal compounds from an insoluble mixture of the metal oxides like Mn (IV) oxide, Fe (III) oxide, Co (III) oxide, Ni (III) oxides etc. and in particular it relates to a process of solubilizing valuable metal ions from a conglomerate of insoluble oxides, i.e. dissolution of a mixed oxide system, and more particularly to a process of leaching Cu, Co and Ni from ocean manganese nodules by L-ascorbic acid.
Present state of the art:
Ocean floor nodules containing significant quantities of metal have been viewed as a source for a number of metals contained therein. The nodules generally contain manganese, iron, copper, nickel, cobalt, zinc, molybdenum, aluminium, magnesium, alkali and other compounds such as clay minerals. Manganese can be present in the nodules generally in an amount of from 10 to 40 weight percent and the nodules have come to be referred to as ocean manganese nodules. Of the many ingredients in the nodules, nickel, copper and cobalt recovery have received major attention as providing economical source of these metals.
Several processes for recovering the values contained in manganese nodules are known. Beck and Messner, in Copper Metallurgy, 1970, pages 70-82 examine the melting of manganese nodules in an electric arc furnace under reducing conditions with simultaneous slag formation of the manganese.
In other known processes, the manganese nodules are decomposed by the sulphate forming roasting or chiorination with gaseous chlorine and/or hydrogen chloride and are then dissolved by leaching with water or diluted sulphuric acid. These methods are discussed in U.S. Bureau of Mines Rept. Invest. 7473, and also substantially corroborated by U.S. patent No. 4,016,055.
Alternative processes have been proposed to selectively reduce the copper, nickel and cobalt contained in the manganese nodules in a first process stage with reduction gas, oil or carbon and to subsequently treat the reduction products in presence of air with an aqueous ammoniacal-ammonium salt solution thus forming amine complexes of copper, nickel and cobalt. U.S. patent Nos. 3,734,715 and 3,788,841 discuss this type of processes. In U.S. Patent No. 3,728,105, there is disclosed a process in which the manganese nodules are subjected directly to an ammoniacal pressure leaching at 300°C.
As claimed in to a proposal made in U.S. Patent No. 3,723,095, the manganese nodules are treated at temperatures up to 60.degree. C with an ammoniacal manganese (II) sulfate solution whereby the values, which form water-soluble amine complexes, are separated from the iron and manganese compounds.
As claimed in to a method described in U.S. patent No. 4,008,076 raw nodules suspension in water and sulphuric acid are heated in a pressure vessel to a temperature between of 150°C and about 300°C to selectively leach nickel, copper, cobalt and zinc from nodules. The nickel, copper and cobalt values are recovered from the metal rich leach solution after separation from residue.
A. Existing hydrometallurgical process using HCI/chlorides etc. has got the
limitations as stated below.
a. Complicated leaching apparatus
b. Highly concentrated leaching agent
c. Expensive reagents
d. Large proportion of acid consumption in case of hydrochloric acid to
form chlorine by product.
e. Polluting effluent gases.
B. Hydrometallurgical processes applying ammoniacal route also have their own
a. Use of high temperature entailing thermal energy cost.
b. Corrosiveness of concentrated alkaline reagents.
c. Complicated process stages needed to circulate ammonia and to
obtain high yields in values.
d. Polluting and hazardous gaseous as well as liquid effluents.
e. High alkali demand for subsequent neutralization steps.
C. Hydrometallurgical processes applying sulphuric acid route are also not free of
a. High temperature and pressure applied therein
b. Polluting effluent chemicals.
Proposed solution (with examples):
The invention will be described as it applies to ocean floor manganese nodules, which comprises of a mixture of insoluble oxides like, Mn (IV) oxide, Ni (III) oxide, Cu (II) oxide and Co (III) oxide and soluble metal values are Co (II), Cu (II) and Ni (II).
An object of the present invention is the provision of an improved process for leaching of ocean manganese nodules to bring valuable metals like copper, cobalt and nickel in solution. 95% Co, 85% Cu and 93% Ni are dissolved within five minutes at room temperature.
Another object of the present invention is to provide a dissolution process for ocean floor nodules comprising of metal oxides that proceeds much more rapidly than other conventional processes.
A further object of the present invention is the provision of a process where no heating of the nodules 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 of 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 applied, 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 mineral acid leaching process.
Yet another object of the present invention is the provision of a process where the solutions used and produced are mild organic 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, glass vessels or glass -lined vessels can also be used.
As claimed in to the present invention, there is provided a method of obtaining an aqueous solution of metal compounds/values from ocean manganese nodules (i.e. a conglomerate of insoluble metal oxides), the metals mostly having a lower oxidation number in the solution than in the insoluble state, comprises treating the nodules at about atmospheric pressure in the presence of a reducing agent at room temperature.
As claimed in to the present invention manganese nodules are leached without any chemical pretreatment operation like prereduction, chlorination or sulphation roasting.
Manganese nodules as recovered from the ocean floor vary considerably in size, and can range from about 0.5 cm to as large as 25 cm in diameter and generally average about 5 cm in diameter. In the practice of this invention it is preferred to reduce the as received nodules to smaller and more uniform size distribution to increase the recovery of metal values. Generally the nodules are comminuted as by crushing preferably to a size between -75, + 50 [im.
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 range of organic reducing agents such as L-ascorbic acid, pyruvic acid, oxalic acid, salicylic acid etc.
The invention is a hydrometallurgical treatment for solubilizing metal values such as copper, cobalt and nickel from the ocean floor nodules.
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.
The major oxide constituent in Ocean floor nodules is manganese dioxide, which acts a matrix for other minor oxides of valuable metals, like copper, cobalt and nickel. So breaking down the MnO.sub.2 phase is a prerequisite to dissolve those valuable metals. The theory of the invention involves use of L-ascorbic acid as a reducing agent to disintegrate manganese dioxide phase by rendering it soluble in aqueous solution.
The reaction is
2Mn0.sub.2 + H2A ^ 2Mn(ll) + A + H.sub.2 O Where A is dehydroascorbic acid.
Once dissolution of MnO.sub.2 takes place the minor metals like copper, cobalt and nickel also come out in the solution.
The preferred temperature of reaction is room temperature.
L-ascorbic acid is added in ratios of molar concentration of MnO.sub.2 in nodules. The rate of reaction is almost independent of molar ratios of oxide and ascorbic acid above 1:2 ratio of manganese oxide: L-ascorbic acid.
Molar ratios manganese dioxide (in the nodules): L-ascorbic acid was tried of 1:2, 1:3, 1:4 and 1:5. The recovery of metal values like copper, cobalt and nickel did not improve further after the first one.
The concentration of solids, that is ground nodules in the ascorbic acid solution, was experimentally varied from 10 g/l to 100 g/l. The extent of dissolution of copper, cobalt and nickel as well as reaction rate was found to be independent of concentration as long as molar ratio of oxide: L-ascorbic acid was varied as claimed inlay.
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 from 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 the invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Following these trials the suitable methods as claimed in to the invention are as follows:
1g of nodules as claimed in to the chemical analysis (presented in Table 1) correspond to 0.0446M MnO.sub.2. So keeping MnO.sub.2: L-ascorbic acid molar ratio at 1:2, 100 ml of 0.0992 M L-ascorbic acid solution is prepared and stirred properly. 1 g of nodules having particle size between +75, -50 i^m range is added to the L-ascorbic acid solution. After 5 minutes the resultant solution was filtered using 45micron Millipore filter paper. After proper washings the residue collected was dried. The dried residue was put in 30 ml 1:1 HCI and heated at 70°C for 30 minutes. The resultant solution was diluted properly and analyzed for Cu, Co. Ni and Mn with help of inductively coupled plasma spectrometry (ICP) method. The metal values left in the residue were subtracted from starting metal concentration obtainable from chemical analysis data for the nodules. The difference gave the metal concentration in filtrate solution.
The filtrate was washed several times with water and mild nitric acid solution. Then the filtrate with the wash water was analyzed for dissolved Mn, Co, Cu and Ni with aid of inductively coupled plasma spectro-photometry (ICP) method.
Both the analytical methods delivered identical results confirming metallurgical balance. All these data are shown in Table 2. As can be observed from the said Table that within a time interval of five minutes 90% Mn, 85% Cu, 93% Co and 95% Ni dissolve into solution.
For the sake of comparison manganese nodule dissolution test was carried out in highly concentrated hydrochloric acid solution for the same time period. 100 ml 11N solution of hydrochloric acid (that is, 1:1 HCI) was prepared. To it was added 1 g manganese nodule powder having particle size in range of +75, -50 |am and the solution was stirred for five minutes. After proper washings with water and dilute nitric acid solution the residue collected was dried and analyzed with aid of Inductively coupled plasma (ICP) spectrometry method following the same procedure as described in the preceding paragraph. Spectrometric analysis confirmed that, only 30% of Mn, 25% Cu, 20% Co, 15% Ni could be dissolved under that extreme condition. The metal recovery values are quite lower compared to the dissolution obtained in our process.
In a slight variation of the process, as described in Examplel, the solid: liquid ratios in the leach pulp was increased from 1:100 to 10:100.
In the previous example 1 g of nodule powder was added to 100 ml of L ascorbic acid solution keeping MnO.sub.2 concentration (in nodules): L-ascorbic acid molar ratio at 1:2. In this case the nodule weight is increased to 5 g and 10 g to observe the effect of solid: liquid ratio. The leaching time was fixed for five minutes.
After 5 minutes the resultant solutions were filtered using 45micron Millipore filter paper. After proper washings the residue collected was dried. The dried residue was put in 30 ml 1:1 HCI and heated at 70°C for 30 minutes. The resultant solution was diluted properly and analyzed for Cu, Co, Ni and Mn with help of inductively coupled plasma spectrometry (ICP) method. The metal values left in the residue were subtracted from starting metal concentration obtainable from chemical analysis data for the nodules. The difference gave the metal concentration in filtrate solution.
The results for 5% pulp density and 10% pulp density experiments are shown in Table 2. Generally in leaching experiments increase in solid: liquid ratio often results a decrease in recovery of metals. But in our process an increase in pulp density upto 10% did not affect the recovery of metals.
Table 1. Partial chemical analysis data of ocean manganese nodules
1. An improved method of obtaining an aqueous solution of a metal compounds
from a mixture of insoluble metal oxides, the metals having a lower oxidation
number in the solution than in the insoluble oxides, comprising treating the mixed
oxide system at about atmospheric pressure, in the presence of a reducing
agent, at room temperature.
2. A method as claimed in claim 1, wherein the metal compounds are mostly
manganese, cobalt, nickel and copper and the mixture of insoluble metal oxides
comprise of Mn (IV) oxide, Co (III) oxide, Ni (III) oxide and Cu (II) oxide.
3. A method as claimed in claim 2, wherein the mixture of insoluble metal oxides
namely, Mn (iV) oxide, Co (III) oxide, Ni (ill) oxide and Cu (II) oxide is ocean floor
4. A method as claimed in 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, nickel and cobalt in solution is carried out by filtration.
5. A method as claimed in any one of claims 1 to 4, wherein the reducing agent is organic in nature.
6. A method as claimed in claim 5, wherein the organic reducing agent is L-ascorbic acid, pyruvic acid, oxalic acid, salicylic acid or an equivalent thereof.
7. A method as claimed in claim 6, wherein the molar ratio of the reducing agent is at least 2:1 with respect to molar concentration manganese dioxide in the mixture of oxides.
8. A method as claimed in claim 6 or 7, wherein the reducing agent is L -
9. A method as claimed in claim any one of claims 1 to 8, wherein the reaction
time is only five minutes.
10. An improved method of obtaining an aqueous solution of metal compounds
from a mixture of insoluble metal oxides substantially as hereinbefore described
and illustrated in the examples.
|Indian Patent Application Number||444/CHE/2003|
|PG Journal Number||20/2006|
|Date of Filing||02-Jun-2003|
|Name of Patentee||M/S. INDIAN INSTITUTE OF SCIENCE|
|Applicant Address||BANGALORE 560 012|
|PCT International Classification Number||C22F 1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|