Patent Application
20090056502
The present invention is related to the field of hydrometallurgical techniques for recovery of nickel and cobalt.
Ionic exchange to recover nickel and cobalt for ecologic, economic and strategic reasons have led to an increasing use of hydrometallurgical techniques in heavy metal recovery. Main methods can be chemical or physical-chemical. Examples of the former are chemical oxidation and chemical precipitation. Examples of the latter are adsorption in activated coal, ionic exchanger and extraction via solvents. There are also physical, electro-chemical and biological methods.
Nickel and cobalt display very similar chemical properties. This facilitates mutual recovery of these metals through precipitation (as sulfides or hydroxides) or through extraction by solvents (in chloride, ammonia or sulfate means). Ionic exchange studies have been intensified, with various promising approaches and results. The ionic exchange technique offers some advantages, such as absence of reagent losses in dragging, superior recovery and removal of smaller concentrations of some metal ions and excess of other metals.
Using polymeric resins in ionic exchange to recover metals (specifically nickel and cobalt) has been widely reported in the literature. Recent technological advances in ionic exchange polymeric resins are increasing its use in hydrometallurgical extraction, especially in the gold and uranium industries. Future use of this technology includes the following upsides: high selectivity for metals of interest, high separation capacity, flexible processing regimens, simple process configuration, a high concentration stage, and a high level of automation. These positive features translate into lesser capital and operating costs. They also lead to lesser environmental impact (less water consumption and an opportunity to recycle used water). Two of the main commercial chelating resins, more frequently cited in technical literature and aimed at selectively recovering nickel and cobalt in an acid medium, are shown below:
Chelating Resins
Chelating polymeric resins are examples of ionic exchangers very efficient in selectively removing heavy metals (such as nickel and cobalt) when compared to other exchangers. These ionic-exchange polymeric resins are copolymers with covalently-linked functional groups, containing one or more donor atoms (Lewis Base). They can form coordinated bindings with most metal ions (Lewis Acid). Coulombic and hydrophobic interactions are also present, but their contribution in high metal-ion selectivity is rather small when compared to the Lewis acid-base interactions. For resins with the iminodiacetic acid functional group, the presence of weak acid clusters leads this exchanger to display high affinity for H+ ions. Hence, the lower the pH, the less selective is recovery of metal ions in view of competition with H+ ions. These resins can normally be regenerated with acid solutions (sulfuric or chloride acid, for instance) and such regeneration is highly efficient.
Chelating exchangers in the bis-picolylamine functional group with nitrogen donor atoms display some little-common properties regarding recovery of aqueous-stage metal ions. As shown by Sengupta, et al., “Metal (II) Ion Binding Onto Chelating Exchanges With Nitrogen Donor Atoms: Some New Observations And Related Implications” Environmental Science Technology, 25, 1991, pp 481-488, specifically for these chelating exchangers, (a) metal ion recovery increases as the concentration of competing Ca2+ and Na2+ ions also increases; (b) metal-removing capacity remains nearly unchanged at low pH values, such as pH=1; (c) regeneration or desorption of metal ions with ammonia is very efficient, while acid regeneration is less effective; (d) both metal cations and anions can be simultaneously removed from the aqueous stage; and (e) due to fimctional clusters of weak acid and weak bases, these exchangers also display affinity with hydrogen ions. Thus, the lower the pH, the lesser will metal ion selective recovery be, given the competition with the H* ions. Sengupta's, supra, complex study of adsorption mechanisms has explained and proven these characteristics.
Two of the main resins dealt with in this text are Dowex M4195® and Amberlite IRC 748®. Both are chelating-type resins with different functional groups and made by different producers.
DOWEX M4195® Resin
Dow Chemical Company has reported a series of chelating resins, among them Dowex M4195®, which is efficient in adsorbing transition metal cations, with high selectivity for copper, nickel and cobalt in the presence of high iron concentrations in a very acid medium (K. C. Jones, et al., “Continuous Recovery from Acidic Leach Liquids by Continuous Ion-Exchange and Electrowinning”, Journal of Metals, pp. 19-25, April 1979). This resin comprises a macroporous polistyrene/divinilbenzene-type copolymer, to which is affixed weak-base derived picolylarnine chelating: bis-picolylamine (L. Rosato, et al., “Separation of Nickel From Cobalt in Sulphate Medium By Ion Exchange”, Hydrometallurgy, 13 (1984), pp. 33-44; R. Grinstead, “Selective Absorporation of Copper, Nickel, Cobalt And Other Transition Metal Ions From Sulfiiric Acid Solution With The Chelating Ion Exchange Resin XFS 4195, Hydrometallurgy, 12 (1984), pp. 387400; and R. Grinstead, “New Developments in the Chemistry of XF54195 and XFS 43084 Chelating Ion Exchange Resins”, Ion Exchange Technology, pp 509-518, 1984).
Selectivity features of these chelating resins suggest their use in some types of hydrometallurgical separation wherein cationic and anionic resins are not always efficient. Although primarily indicated for copper liquor processing, a later study involving calculation of its adsorption coefficients revealed that these resins can be potentially effective in recovering transition metal sulfates, such as nickel and cobalt—see Table 1 (from Rosato et al., supra).
In the specific case of M4195, its overall structure is based on the weakly-basic bis-picolilamine chelating group, which is covalently linked to the polestirene-divinilbenzene copolymer (see Table 2).
M4195 is the resin most often cited in the literature. However, no record was found of Ni/Co recovery in nickel lateritic ore treatment processes.
M4195, resin's functional clustering acts as a complexant agent more efficient for nickel, when compared to other resins, in the entire pH range. However, its selectivity for cobalt is considerably less. Cobalt, which is swiftly adsorbed in initial loading (charging), soon desorbs, due to nickel's preferential selectivity. However, the higher the pH is, the easier it is to simultaneously recover Ni and Co. In the M4195 resin, Cu and Ni are effectively adsorbed, even at low pH values, in the following adsorption order: Cu>Ni>Co>Zn>Al. ( S. Nagib, et al., “Recovery of Ni From A Large Excess of Al Generated from Spent Hydrodesulffirization Catalyst Using Picolylamine Type Chelating Resin And Complexane Types of Chemcially Modified Chitosan”, Hyrdometallurgy, 51 (1999), pp 73-85).
AMBERLITE C748® Resin
Amberlite IRC 748® is a chelating-type resin with high selectivity for heavy metal cations, if compared to alkaline metals. Selectivity is reached by the iminodiacetic acid functional group chemically linked to a macroreticular matrix. According to its maker, Rohin & Haas Company, given its high selectivity for heavy metals and outstanding kinetic performance, this resin can remove metals from the solution, even in the presence of high concentration of calciun and sodium salts. Moreover, its macroreticular structure is highly resistant to osmotic shock and features excellent physical stability. Table 3 below shows the structure of the iminodiacetic acid ftnctional group and some physical properties.
It is possible to find in literature references to the Amberlite IRC 748® resin regarding studies of nickel adsorption in acid medium. In general, selectivity in adsorption follows the following order: Na+<<Ca2+<Mn2+<Fe2+<Co2+<Cd2+<Zn2+<Ni2+<Pb2+<Cu2+<Hg2+<Fe3+. Affinity for ions H+ in pH 4 lies between Pb2+ and Cu2+. Consequently, for metals with selectivity below Cu2+, the resin must be used as Na+, for instance. In pH2, the resin is displayed as H+ in view of medium acidity and, in this case, preferably removes Fe3+, Cu2+ and Hg2+.
Resin-in-Pulp “(RIP)” Technology
Industrial units which use hydrometallurgical processing to recover nickel and cobalt include a countercurrent multi-stage settling circuit, which is responsible for separating solid-liquid and washing solids, in order to maximize nickel and cobalt recoveries from the leaching effluent pulp. Towards this purpose, a series of corrosion-resistant thickeners is used. However, they involve high capital and operating cost, occupy large areas and consume significant amounts of washing water. An option replacing costly countercurrent settlement is to use a RIP system. This is used to recover nickel and cobalt from leached pulp, with no need to use thickeners. Next, nickel and cobalt would be individually recovered, separated and purified via continuous ionic exchange in countercurrent, for instance, based on concentrated eluant solution. This eluant solution could be based on chloride or sulfide. Final recovery could occur through electrolysis, pyrohydrolysis, reduction via hydrogen or precipitation methods, among other forms.
RIP technology can be used to enhance pre-existing systems or to replace conventional technologies. In cases wherein process engineering is taken into account, this technology could substitute counter current decantation (“CCD”) technology and reduce environmental impact. In operating plants using the CCD process, RIP technology can improve the pre-existing technology, increase metal recovery and improve their purity, in addition to reducing environmental impact This alternative, coupled to the solid-liquid separation circuit, becomes particularly attractive in cases wherein lateritic ores are hampered by constrains (long deposition time) to CCD circuit processing, triggering metal losses in residues.
RIP is a process in which the ionic exchange polymeric resin directly contacts the leaching pulp in countercurrent. Sieve screening separates resin from pulp, and metals in the resin are recovered through elution. This system is commonly used in commercial uranium recovery, especially for low-grade and hard-to-settle pulps. The carbon-in-pulp (“CIP”) process has a similar concept, where coal (carbon) performs a role similar to resin's in the RIP process. RIP technology's chief characteristic is the “sorption-leaching” phenomenon. In it, ionic exchange continuously removes nickel and cobalt from the liquid phase, allowing subsequent leaching. Therefore, an additional amount of nickel and cobalt is recovered from the pulp's solid portion, which is normally not recovered in other processes.
Continuous Ionic Exchange Technology
Continuous ionic exchange (IONEX) technology involves continuous adsorption in countercurrent flow, through one single multi-opening valve. IONEX technology offers lower costs and greater separation efficiency in industrial processes, in view of the following factors:
Enhanced productivity—The continuous ionic exchange system provides more efficient and productive recovery, if compared to non-continuous systems, given its real countercurrent configuration. Previous experiences with processes such as lysine, potassium, salt and antibiotic production have shown that production can increase in the 5% to 10% range when the IONEX system is used. Enhanced productivity generates further recoveries and increased revenue.
Enhanced purity—The continuous ionic exchange system offers separation with high-purity products, given the higher efficiency of the countercurrent operation. The solution's high purity reduces the need for additional purification, thus reducing investment and operating costs.
Higher reliability—The continuous ionic exchange systems offers stronger reliability based on fewer mobile mechanical parts, if compared to the other systems. Non-continuous systems need countless automatic valves, and mobile resin beds needs a carrousel-type systems and flexible connections. Higher reliability leads to more availability, which, in turn, is conducive to additional production and lower maintenance cost. The internal disk is the only mobile component in the IONEX system. Systems with numerous automatic valves and carrousel systems with a rotary platform to physically move the resin's bed are eliminated.
More flexibility—The continuous ionic exchange system makes a large number of functions simultaneously possible, given its continuous operation, thus allowing the system to enjoy great flexibility. The IONEX system can be adjusted in a pre-existing fixed resin bed or in a mobile bed system. Locating existing resin vases is not relevant, which translates into process advantages and less operating costs, with no need of a full upgrade.
Higher yield—The continuous ionic exchange system leads to superior yielding because of longer resin durability, if compared to other systems. Yield-per-resin life increases due to shorter cycle times. Experience shows that such increase can be at least 100% and, in some cases, as high as 1000%. Shorter cycles prevent long-period resins from impurity exposure. Effective resin duration is extended and significantly reduces operating costs.
Less resin inventory—The continuous ionic exchange system uses less resin, if compared to other systems. Resin inventory can be reduced by 80% vis-a-vis conventional systems, tantamount to significant savings in investment and operations.
Less water treatment—The continuous ionic exchange system uses less water, in view of its countercurrent washing stage. This upside generates significant investment & operating savings, in preparing and treating washing and cleaning solutions.
Less effluent treatment—The continuous ionic exchange system generates fewer effluents because of its countercurrent washing. Fewer effluents require smaller systems for their treatment, which reduces project costs.
Less use of space—The continuous ionic exchange system liberates over 800% of the available space, if compared to conventional systems. The need for less resin in stock, smaller resin beds, fewer mobile mechanical parts, reduction of ancillary systems significantly reduce space necessity and investment costs.
Continuous ionic exchange operations involve stages of adsorption, elution and regeneration, plus intermediate washing stages. Its advantages, when compared to other adsorption systems are clear. This makes it a promising process option. The upsides of Dow Chemical's resin are well known and ensure a high potential of success in selective nickel recovery in the presence of impurities and under great-acidity conditions.
It should be noted that the state of the art comprises several documents within the same field of technology related to the hydrometallurgical techniques for recovery of nickel and cobalt but none of them suggest the the present invention.
WO 01/29276A1 “Resin-In-Pulp Method For Recovery Of Nickel And Cobalt From Oxidic Ore Leach Slurry” to W. Duyvesteyn, et al. refers to a process for the recovery of nickel and cobalt from nickeliferous oxide ore leach slurry by ion exchange. It also teaches that nickel and/or cobalt are recovered by known processes. Thus, the proposed process fails in recovering precipitated cobalt and nickel as oxide with HCl regeneration.
WO 962/0291 “Recovery Of Nickel And Cobalt From Laterite Ores” to W. Duyvesteyn, et al. describes a process for selectively recovering nickel by ion exchange absorption from a Ni/Co sulfuric acid feed solution obtained from limonite ore which is pressure leached with sulfuric acid and then neutralized and solid/liquid separated, containing nickel in the range of about 0.5 to 40 gpl and cobalt in the range of about 0.01 to 2 gpl as sulfates. The document describes that the absorbed nickel is stripped from said resin with sulfuric acid to form a nickel sulfate solution characterized by a nickel to cobalt ratio of at least about 50:1 suitable for the recovery of substantially pure nickel by electrolysis. Thus, the document refers to the recovery of nickel merely by electrolysis, which is a well known method for this specific technology and it also uses the solidaiquid separation.
WO 2007/087698 “Hybrid Process Using Ion Exchange Resins In The Selective Recovery Of Nickel And Cobalt From Leaching Effluents” to R. Costa, et al. (and the present co-inventor) is directed to a hybrid process using ion exchange resins in the selective recovery of nickel and cobalt of leaching effluents that is comprised of the steps of processing the. laterite ore, which is then treated through leaching (either atmospheric or under pressure), considering solutions from the solid-liquid separation step of existing plants already in operation as well, in a way that the downstream process comprises an ion exchange hybrid circuit. Even though the document is related to the recovery of nickel and cobalt, it still mentions the solid-liquid separation and does not suggest stages of obtaining nickel oxide.
WO 2006/069416 “Extraction Of Nickel And Cobalt From A Resin Eluate Stream” to D. Krebs is directed to recovery of nickel and cobalt from acidic resin eluate containing Ni and Co, treating the eluate with immiscible organic reagent to selectively absorb the majority of Co, and portion of any copper, zinc and manganese present in the eluate, but it does not mention the recovery of nickel as oxide and the method for separating both metals used therein is by the traditional extraction-by-solvents methods.
US 2006/0024224 A1 “Method For Nickel And Cobalt Recovery From Laterite Ores By Combination Of Atmospheric And Moderate Pressure Leaching” to D. Neudorf, et al., describes a process for leaching laterite ores containing limonite and saprolite. Sufficient mineral acid is added to a slurry of limonite, which is leached at atmospheric pressure to dissolve most of the soluble non-ferrous metals and soluble iron. After adding saprolite the slurry is further leached at a temperature above the normal boiling point and at a pressure above atmospheric pressure for a time sufficient to leach most of the contained nickel in the saprolite and to precipitate most of the iron in solution. Although dealing with the same technology it teaches that nickel and/or cobalt can be recovered by several types of methods, without defining which would be the best one for the recovery, apart from the fact that it uses the traditional method of autoclave to leach most of the contained nickel in the saprolite ore and to precipitate most of the iron in solution.
U.S. Pat. No. 3,839,168 “Method For Producing High-Purity Nickel From Nickel Matte” to L. Gendor et al.; WO 05/045078 “A Method For The Removal Of Copper From A Zinc Sulphate Solution” to L. Lehtinen, et al., U.S. Pat. No. 6,524,367 “Hydrometallurgical Process For The Recovery Of Nickel And Cobalt By Ammoniacal Leaching” to J. Suarez, et al.; WO 01/32943 “Atmospheric Leach Process For The Recovery Of Nickel And Cobalt From Limonite And Saprolite Ores” to J. Arrayo et al., also pertain to the same general technology of recovery of nickel and cobalt which can be encountered in the state of the art. But all of them use the same traditional and classical methods for doing so, comprising heavy equipments and more expensive solutions.
The present invention deals with a hydrometallurgical process to produce nickel as hydroxide, oxide or cathode and produce cobalt preferably as sulfides. The present invention is particularly adequate to process eluate containing nickel and cobalt. Eluates are solutions obtained from elution of ionic exchange resins, loaded (charged) in the RIP (resin-in-pulp) process of ionic exchange, to recover nickel and cobalt from effluent pulps in acid leaching. Following nickel and cobalt recovery in a RIP circuit, they are separated from each other via a continuous ionic exchange process, after which the nickel eluate is formed to produce nickel as nickel oxide by a pyrohydrolysis process, which is the key stage of the invention.
In the drawings:
In the drawings:
The present invention, in accordance with
As shown in
It is the only know operation so far that can truly operate in a continuous way. All ion exchange systems nowadays only load in a continuous way, having their desorption stage done in batches. IONEX has a unique valve that allows one to easily change flows, switching from a loading step to a elution step faster and easily. This new method allows one to separate nickel and cobalt, using different loading (charging) and elution times.
Flow rates, pH of operation and other process variables are more dependent on which kind of resin is employed and not by the equipment itself. Therefore, these parameters cannot be defined without choosing a resin type.
Eluate obtained in the previous RIP operation contains high concentrations of nickel and cobalt, which must be separated through continuous ionic exchange and countercurrent systems. Nickel and cobalt are separated through the use of ionic exchange resins for selective nickel recovery. The resin adsorbs all or most of the nickel dissolved in solution, leaving all or most of the remaining cobalt in solution with impurities. Cobalt is then precipitated as sulfide, hydroxide or carbonates, and nickel is eluted from the resin and recovered in a wide-range of different products, as precipitate in the form of hydroxide, oxide via pyrohydrolysis, with HCl regeneration or electro-recovered as cathode nickel. The present process leads to expectations of efficient recovery of metals of interest, selective removal of low concentrations of metal ions, such as cobalt, preferably in excess of other metals, high loading (charging), high mechanical resistance which reduces friction-caused losses, swift elution, and minimal or no loss due to organic material contamination.
Unless otherwise indicated, the adverb “about” before a series of values will apply to each value in the series.
Pyrohydrolysis may be regarded as a key stage in the present invention. Indeed, this stage generates the end product—nickel as oxide—and chloride acid is regenerated in order to be reused in the process, preferably in elution of the loaded (charged) resin. This process has two major advantages. First, chloride acid regeneration is an environmental necessity. In many hydrometallurgical processes, it is essential to recover the leaching agent (HCl, Cl2, FeCl3), since discarding it with dissolved metals is economically and ecologically unacceptable. The second major advantage is the economic savings obtained in acid regeneration, as reagents' operation cost is minimized. High recovery (roughly 99%) of high-purity acid is common, and this is vitally important if the objective is to sell chloride acid. Some hydrometallurgical processes have metal oxide as the desired end product and HCl regeneration as the byproduct. In some cases, a concentrated NiCl2 solution can be produced. This solution can undergo pyrohydrolysis, generating NiO and HCl, or undergo electrolysis, generating metallic nickel and chloride gas. In order to obtain metal from NiO, oxide must be reduced with H2 at a 750° C. temperature.
An electrolysis upside is producing metallic nickel in one single stage. However, electrolysis has some drawbacks: chloride necessary for HCl production is generated in small amounts in many anodes, and it must be carefully collected and treated. Electric power generation is costly and its efficiency is only 35%. Pyrohydrolysis produces nickel oxide in one single stage, but it also simultaneously produces chloride gas, which is absorbed in water. Metal reduction can be carried out in a separate furnace, with H2 stoichiometric addition. In such cases, granular nickel oxide is preferred, because in its fine form it can agglomerate around the reduction furnace. Nickel pyrohydrolysis occurs at relatively high temperatures, above 727° C. Thermodynamic data reveal that, if the temperature drops down to 700° C., reverse NiO reaction occurs, generating NiCl2. The exact temperature depends on the HCl/H2O ratio in the gas. In partial HCl high pressure, reverse reaction forming NiCl2 occurs at temperatures above 700° C.
The present invention refers, specifically, to a hydrometallurgical process for recovery of nickel and cobalt, as follows:
Flexibility, high recovery, low investment and operating costs, electric power savings result from the technological process herein proposed.
Even though it is not industrially used in nickel ore processing, RIP (resin-in-pulp) ionic exchange must be used to recover nickel and cobalt in neutralized leaching effluent pulps. Leaching may occur under atmospheric conditions and at temperature below 100° C. or under high pressure and at high temperature. RIP is a three-stage circuit.
In adsorption, nickel and cobalt are selectively recovered in mechanically stirred or in air-stirred (pachuca) vats. Resins suggested for this type of use are those in iminodiacetic and picolylamine groups. Contact between resin and pulp occurs in countercurrent, with intermediate sieves between the vats, for the sake of phase separation. Effluent resin in the first adsorption vat is withdrawn from the circuit, taken to removal of aggregate solids, and transferred to the elution circuit. Elution of resin-loaded metals that can occur selectively and in multiple stages must occur with sulfuric, chloride or nitric acid, at a concentration range of 50 g/L-150 g/L approximately. Regeneration is the stage wherein the eluted resin is placed in contact with a reagent (such as soda or limestone), to be regenerated and resume calcium or sodium forms.
While in accordance with the provisions of the statute, there is illustrated and described herein specific embodiments of the invention. Those skilled in the art will understand that changes may be made in the form of the invention covered by the claims and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.
This application claims priority from U.S. provisional applications 60/968,614 and 60/968,619 both filed on Aug. 29, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60968614 | Aug 2007 | US | |
| 60968619 | Aug 2007 | US |
