WO2021094823A1

WO2021094823A1 - Processes for recovering iodine from aqueous leaching product streams containing gold

Info

Publication number: WO2021094823A1
Application number: PCT/IB2020/000878
Authority: WO
Inventors: Duane Nelson; Mohammad DOOSTMOHAMMADI; Ishwinder Singh Grewal; Hanif JAFARI
Original assignee: Enviroleach Technologies Inc.
Priority date: 2019-11-12
Filing date: 2020-11-04
Publication date: 2021-05-20

Abstract

Processes for recovering iodine from solid materials in which copper is present are performed by combining the solid material with a basic solution having a pH greater than 10 to solubilize and remove iodine from the solid material, thereby forming an iodine recovery stream.

Description

PROCESSES FOR RECOVERING IODINE FROM AQUEOUS LEACHING PRODUCT STREAMS CONTAINING GOLD

REFERENCE TO RELATED APPLICATION This application is being filed on November 4, 2020, as a PCT International Patent

Application and claims the benefit of U.S. Provisional Patent Application No. 62/934,029, filed on November 12, 2019, the disclosure of which is incorporated herein by reference in its entirety. FIELD OF THE INVENTION

The present disclosure generally relates to the recovery of iodine from a solid material that comprises a copper compound containing iodine, and more particularly, to the recovery of iodine from a solid fraction separated from a pregnant leach solution that contains gold and other precious metals.

BACKGROUND OF THE INVENTION

Iodine-based leaching solutions can be used for the extraction of gold and other precious metals from various substrates, such as mining ores and electronic waste. It would be beneficial to develop processes that can recover the iodine that is used in the leaching and extraction of precious metals from these substrates. Accordingly, it is to these ends that the present invention is generally directed.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify required or essential features of the claimed subject matter. Nor is this summary intended to be used to limit the scope of the claimed subject matter.

The invention disclosed herein generally relates to processes for recovering iodine from solid materials in which copper is present. One such process is directed to recovering iodine from an aqueous mixture of a solid fraction and a pregnant leach solution, in which the solid fraction comprises a copper compound containing iodine and the pregnant leach solution comprises gold and iodine. This process can comprise (i) contacting the mixture with a basic material having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the pregnant leach solution, wherein the basic material comprises a basic solid and/or a basic solution, and (ii) separating at least a portion of the pregnant leach solution from the solid fraction to form an iodine recovery stream.

Another process disclosed herein for recovering iodine from a solid fraction comprising a copper compound containing iodine can comprise (a) contacting, in an aqueous medium, the solid fraction with a basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous medium, and (b) separating at least a portion of the aqueous medium from the solid fraction to form an iodine recovery stream.

Yet another process for recovering iodine from a solid fraction comprising a copper compound containing iodine can comprise (A) contacting the solid fraction with an aqueous basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous basic solution, and (B) separating at least a portion of the aqueous basic solution from the solid fraction to form an iodine recovery stream. Both the foregoing summary and the following detailed description provide examples and are explanatory only. Accordingly, the foregoing summary and the following detailed description should not be considered to be restrictive. Further, features or variations may be provided in addition to those set forth herein. For example, certain aspects and embodiments may be directed to various feature combinations and sub-combinations described in the detailed description.

BRIEF DESCRIPTION OF THE FIGURE FIG. 1 is a schematic flow diagram illustrating a representative precious metal leaching process with iodine recovery.

DEFINITIONS

To define more clearly the terms used herein, the following definitions are provided. Unless otherwise indicated, the following definitions are applicable to this disclosure. If a term is used in this disclosure but is not specifically defined herein, the definition from the IUPAC Compendium of Chemical Terminology, 2^nd Ed (1997), can be applied, as long as that definition does not conflict with any other disclosure or definition applied herein, or render indefinite or non-enabled any claim to which that definition can be applied. To the extent that any definition or usage provided by any document incorporated herein by reference conflicts with the definition or usage provided herein, the definition or usage provided herein controls.

Herein, features of the subject matter can be described such that, within particular aspects and/or embodiments, a combination of different features can be envisioned. For each and every aspect, and/or embodiment, and/or feature disclosed herein, all combinations that do not detrimentally affect the designs, processes, and/or methods described herein are contemplated with or without explicit description of the particular combination. Additionally, unless explicitly recited otherwise, any aspect, and/or embodiment, and/or feature disclosed herein can be combined to describe inventive features consistent with the present disclosure.

While compositions and processes are described in terms of “comprising” various components or steps, the compositions and methods also can “consist essentially of’ or “consist of’ the various components or steps, unless specifically stated otherwise.

The terms “a,” “an,” and “the” are intended to include plural alternatives, e.g., at least one, unless otherwise specified. For instance, the disclosure of “a basic material” and “a metal” is meant to encompass one, or mixtures or combinations of more than one, basic material and metal, respectively, unless otherwise specified.

All “ppm” quantities disclosed herein refer to ppm by weight, unless specifically stated otherwise.

Generally, groups of elements are indicated using the numbering scheme indicated in the version of the periodic table of elements published in Chemical and Engineering News, 63(5), 27, 1985. In some instances, a group of elements can be indicated using a common name assigned to the group; for example, alkali metals for Group 1 elements, alkaline earth metals for Group 2 elements, transition metals for Group 3-12 elements, and halogens or halides for Group 17 elements.

For any particular compound or group disclosed herein, any name or structure presented is intended to encompass all conformational isomers, regioisomers, and stereoisomers that can arise from a particular set of substituents, unless otherwise specified. For example, a general reference to pentane includes n-pentane, 2-methyl-butane, and 2,2- dimethylpropane, and a general reference to a butyl group includes an n-butyl group, a sec- butyl group, an iso-butyl group, and a t-butyl group. The name or structure also encompasses all enantiomers, diastereomers, and other optical isomers whether in enantiomeric or racemic forms, as well as mixtures of stereoisomers, as would be recognized by a skilled artisan, unless otherwise specified. The terms “contacting” or “combining” are used herein to describe methods and processes in which the materials or components are contacted or combined together in any order, in any manner, and for any length of time, unless otherwise specified. For example, the materials or components can be blended, mixed, slurried, dissolved, reacted, treated, compounded, impregnated, washed, or otherwise contacted or combined in some other manner or by any suitable method or technique.

Various numerical ranges are disclosed herein. When a range of any type is disclosed or claimed herein, the intent is to disclose or claim individually each possible number that such a range could reasonably encompass, including end points of the range as well as any sub-ranges and combinations of sub-ranges encompassed therein, unless otherwise specified. As a representative example, the present application discloses that the molarity of the basic solution often can fall within a range from about 0.5 to about 2.5 M in certain aspects. By a disclosure that the molarity of the basic solution can be in a range from about 0.5 to about 2.5 M, the intent is to recite that the molarity can be any molarity within the range and, for example, can be equal to about 0.5 M, about 1 M, about 1.5 M, about 2 M, or about 2.5 M. Additionally, the molarity can be within any range from about 0.5 to about 2.5 M (for example, the molarity can be in a range from about 0.75 to about 2.25 M), and this also includes any combination of ranges between about 0.5 and about 2.5 M (for example, the molarity can be in a range from about 0.5 to about 1.5 M, or from about 2 to about 2.5 M). Further, in all instances, where “about” a particular value is disclosed, then that value itself is disclosed. Thus, the disclosure that the molarity can be from about 0.5 to about 2.5 M also discloses a molarity from 0.5 to 2.5 M (for example, from 0.75 to 2.25 M), and this also includes any combination of ranges between 0.5 and 2.5 M (for example, the molarity can be in a range from 0.5 to 1.5 M, or from 2 to 2.5 M). Likewise, all other ranges disclosed herein should be interpreted in a manner similar to this example.

The term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement errors, and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such. The term “about” also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term “about,” the claims include equivalents to the quantities. The term “about” can mean within 10% of the reported numerical value, preferably within 5% of the reported numerical value.

Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the typical methods and materials are herein described.

All publications and patents mentioned herein are incorporated herein by reference for the purpose of describing and disclosing, for example, the constructs and methodologies that are described in the publications, which might be used in connection with the presently described invention.

DETAILED DESCRIPTION OF THE INVENTION

Iodine-based leaching of precious metal-containing substrates can produce a pregnant leach solution containing the desirable precious metal (e.g., gold) and a solid fraction, which can comprise copper compounds containing iodine, such as copper iodide. Often, the precious metal-containing substrate (such as mining ores and electronic waste) contains copper minerals or elemental copper that are leached and solubilized in the iodine- based leaching solution containing iodide ions. While not wishing to be bound by the following theory, it is believed that some of the iodide precipitates from solution due to the formation of an insoluble copper iodide (Cul) species according to the following reaction:

2Cu²⁺ (aq) + 4T (aq) 2CuI (s) +h (aq).

When the pregnant leach solution is separated from the solid fraction, the copper iodide remains with the solid fraction, and thus the iodine contained therein is lost and discarded with the residual solid fraction. However, iodine and its salts are relatively expensive, so it is important to recover this iodine. Beneficially, the processes disclosed herein can recover a large portion of this otherwise unrecoverable iodine.

Again, while not wishing to be bound by the following theory, it is believed that the use of basic hydroxides can liberate iodine from the solid copper iodide, according to the following reaction:

2CuI (s) + 20H (aq) Cu₂0 (s) + 2T (aq) + H₂0.

By contacting the leached solid fraction with an appropriate hydroxide solution, advantageously, the iodine is liberated into solution and recovered, while the copper remains in the solid fraction as an oxide, such as copper oxide.

Accordingly, disclosed herein are various processes for recovering iodine. A first process is directed to recovering (or removing) iodine from an aqueous mixture of a solid fraction and a pregnant leach solution (e.g., a slurry of the solid fraction in the pregnant leach solution), wherein the solid fraction comprises a copper compound containing iodine and the pregnant leach solution comprises gold and iodine. The first process can comprise (or consist essentially of, or consist ol) (i) contacting the mixture with a basic material having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the pregnant leach solution, wherein the basic material comprises a basic solid and/or a basic solution, and (ii) separating at least a portion of the pregnant leach solution from the solid fraction to form an iodine recovery stream. A second process for recovering (or removing) iodine from a solid fraction comprising a copper compound containing iodine can comprise (or consist essentially of, or consist ol) (a) contacting, in an aqueous medium, the solid fraction with a basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous medium, and (b) separating at least a portion of the aqueous medium from the solid fraction to form an iodine recovery stream. A third process for recovering (or removing) iodine from a solid fraction comprising a copper compound containing iodine can comprise (or consist essentially of, or consist ol) (A) contacting (or washing) the solid fraction with an aqueous basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous basic solution, and (B) separating at least a portion of the aqueous basic solution from the solid fraction to form an iodine recovery stream. Generally, the features of the first process, the second process, and the third process (e.g., the components and/or features of the solid fraction, the copper compound containing iodine, the pH, the basic material or basic solution, the components and/or features of the iodine recovery stream, and the process conditions under which the respective steps of each process are conducted, among others) are independently described herein, and these features can be combined in any combination to further describe the disclosed first process, second process, and third process.

Referring now to the first process for recovering (or removing) iodine from an aqueous mixture of a solid fraction and a pregnant leach solution - wherein the solid fraction can comprise a copper compound containing iodine and the pregnant leach solution can comprise gold and iodine - the first process can comprise the steps of (i) contacting the mixture with a basic material having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the pregnant leach solution, wherein the basic material comprises a basic solid and/or a basic solution, and (ii) separating at least a portion of the pregnant leach solution from the solid fraction to form an iodine recovery stream. While not being limited thereto, the aqueous mixture of the solid fraction (comprising a copper compound containing iodine) and the pregnant leach solution (comprising gold and iodine) can be the result of contacting a solid substrate comprising a precious metal with an aqueous-based leaching solution containing iodine (e.g., the iodine-based leaching of gold from a precious metal-containing substrate).

Prior to step (i), the pregnant leach solution often can contain from about 1 to about 10,000 mg/L of gold, from about 1 to about 1000 mg/L of gold, or from about 5 to about 500 mg/L of gold, although not limited thereto. The gold concentration is on an elemental basis. As one of skill in the art would readily recognize, the gold often will be present in the solution as an ionic complex.

Additionally or alternatively, prior to step (i), the pregnant leach solution can contain any suitable amount of iodine, such as (on an elemental basis) from about 1 to about 500 g/L of iodine, from about 1 to about 100 g/L of iodine, or from about 5 to about 50 g/L of iodine. Further, the pregnant leach solution can contain palladium and/or platinum, in addition to gold and iodine. Prior to step (i), the majority of the pregnant leach solution typically is water, such that the pregnant leach solution contains at least about 50 wt. % water in one aspect, at least about 75 wt. % water in another aspect, and at least about 90 wt. % water in yet another aspect, and can contain up to about 95-99 wt. % water in some instances.

The basic material in step (i) can be a basic solid, a basic solution, or a combination thereof. Thus, in one aspect, the basic material can comprise the basic solid, and the basic solid can comprise solid NaOH and/or solid KOH, for example. In this aspect, the solid base product can be combined with the aqueous mixture of the solid fraction and the pregnant leach solution. In another aspect, the basic material can comprise the basic solution, which can be a hydroxide-based solution, for example. In this aspect, the liquid base solution can be combined with the aqueous mixture of the solid fraction and the pregnant leach solution. If desired, in yet another aspect of this invention, both a basic solid and a basic solution can be combined with the aqueous mixture. Regardless of the form of the basic material, step (i) typically comprises agitating the mixture and the basic material, so as to improve the contact between the basic moiety and the copper compound in the solid fraction.

Referring now to the second process and the third process, the second process for recovering (or removing) iodine from a solid fraction comprising a copper compound containing iodine can comprise the steps of (a) contacting, in an aqueous medium, the solid fraction with a basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous medium, and (b) separating at least a portion of the aqueous medium from the solid fraction to form an iodine recovery stream. In the second process, step (a) can comprise mixing or agitating the solid fraction with the basic solution in the aqueous medium in a tank or other suitable vessel.

The third process for recovering (or removing) iodine from a solid fraction comprising a copper compound containing iodine can comprise the steps of (A) contacting (or washing) the solid fraction with an aqueous basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous basic solution, and (B) separating at least a portion of the aqueous basic solution from the solid fraction to form an iodine recovery stream. In the third process, step (A) can comprise washing the solid fraction with the aqueous basic solution, with or without agitation. For instance, the third process can comprise washing a cake of the solid fraction with the aqueous basic solution, followed by filtration.

Prior to step (a) and step (A), the second and third processes can further comprise a step of contacting a solid substrate comprising a precious metal with an aqueous-based leaching solution containing iodine to form the pregnant leach solution and the solid fraction (e.g., the iodine-based leaching of gold from a precious metal-containing substrate). Generally, prior to step (a) and step (A), at least a portion of the solid fraction is separated from the pregnant leach solution before treatment in the second and third processes, such that in some aspects, only the solid fraction is treated with the basic solution in the second and third processes (not the pregnant leach solution), in contrast with the first process in which an aqueous mixture of the solid fraction and the pregnant leach solution is treated with the basic material.

As it pertains to the first process, the second process, and the third process, the copper compound containing iodine - in the solid fraction - can comprise copper iodide. While not being limited thereto, the solid fraction often contains from about 0.1 to about 80 wt. % copper, from about 1 to about 40 wt. % copper, from about 2 to about 25 wt. % copper, or from about 0.5 to about 5 wt. % copper. As above, the copper concentration is on an elemental basis, and this is prior to step (i), step (a), and step (A). Additionally or alternatively, the solid fraction can contain - prior to step (i), step (a), and step (A) - from about 0.1 to about 40 wt. % iodine, from about 0.1 to about 15 wt. % iodine, from about 0.1 to about 5 wt. % iodine, or from about 0.5 to about 10 wt. % iodine (on an elemental basis). Depending upon the source of the precious-metal containing solid substrate prior to leaching, the resulting solid fraction can contain many other materials. In some aspects, the solid substrate can comprise a mining ore, while in other aspects, the solid substrate can comprise electronic waste. Thus, the solid fraction composition can vary significantly. For instance, the solid fraction can further comprise other metals (non-precious metals), illustrative examples of which can include iron, nickel, zinc, aluminum, and the like, as well as combinations thereof. Particularly when the solid substrate comprises a mining ore, the solid fraction can be further comprise any suitable minerals, such as an elemental mineral (e.g., copper and lead), a silicate mineral (e.g., mica and quartz), an oxide mineral (e.g., bauxite and hematite), a sulfide mineral (e.g., pyrite and chalcopyrite), a sulfate mineral (e.g., barite and gypsum), a halide mineral (e.g., halite and fluorite), a carbonate mineral (e.g., calcite and malachite), and/or a phosphate mineral (e.g., turquoise and apatite), and this includes various combinations of these mineral types in any amount. If the solid substrate comprises electronic waste, there are often various plastic components present, and therefore, the solid fraction can contain any number of plastic materials.

The basic solution that can be used in step (i), step (a), and step (A) is not particularly limited, but often comprises one or more of LiOH, NaOH, KOH, and/or NH4OH; alternatively, NaOH and/or KOH; alternatively, NaOH; or alternatively, KOH. Likewise, the molarity of the basic solution is not limited, but often ranges from about 0.1 to about 5 M; alternatively, from about 0.5 to about 2.5 M; or alternatively, from about 1 to about 2 M. The pH of the basic material or basic solution generally is at least about 10, but in some aspects of this invention, can be at least about 11, at least about 12, at least about 13, or in a range from about 12 to about 14.

The amount of the basic material (or basic solution) is not particularly limited, but generally, the molar ratio of base equivalents of the basic material or the basic solution - used in step (i), step (a), and step (A) - to iodine present in the solid fraction is at least about 1:1. More often, the molar ratio of base equivalents of the basic material or the basic solution to iodine in the solid fraction can range from about 2: 1 to about 50:1; alternatively, from about 2:1 to about 10:1; or alternatively, from about 3:1 to about 25:1. Optionally, any excess basic material or excess basic solution can be recycled, and used again in the first process, the second process, and the third process.

Any suitable temperature and pressures conditions can be used for each step in the first process, the second process, and the third process. Typical temperatures for each step, independently, can be in a range from about 10 °C to about 85 °C, from about 15 °C to about 70 °C, from about 20 °C to about 50 °C, or from about 20 °C to about 40 °C. Thus, in some aspects, the first process, the second process, and the third process can be conducted at ambient temperature. Typical pressures for each step, independently, often can range from ambient pressure to about 200 psig (1378 kPag), or from ambient pressure to about 100 psig (689 kPag).

The duration of each step in the first process, the second process, and the third process also is not particularly limited, but generally, each step can be conducted - independently - for a time period in a range from about 30 sec to about 24 hr, from about 30 sec to about 2 hr, from about 1 min to about 6 hr, from about 1 min to about 1 hr, from about 1 min to about 30 min, or from about 1 min to about 15 min, and the like.

Referring now to step (ii), step (b), and step (B) of the first process, the second process, and the third process, respectively, these steps are separating steps. Step (ii) is directed to separating at least a portion of the pregnant leach solution from the solid fraction to form an iodine recovery stream, whereas step (b) is directed to separating at least a portion of the aqueous medium from the solid fraction to form an iodine recovery stream, and step (B) is directed to separating at least a portion of the aqueous basic solution from the solid fraction to form an iodine recovery stream. Any suitable technique can be used in these separating steps. Such techniques can include extraction, filtration, evaporation, distillation, draining, pressing, centrifuging, and the like, or any combination of two or more of these techniques. For instance, in the second process, step (b) can utilize filtration and/or centrifuging to separate at least a portion of the aqueous medium from the solid fraction to form the iodine recovery stream.

In accordance with particular aspects of this invention, the first process, the second process, and the third process can comprise at least two contacting steps and at least two separating steps, performed in any order. Thus, the solid fraction can be treated once, twice, three times, and so forth, with the basic material or the basic solution in order to increase the recovery of iodine in the respective process.

Referring to the second process and the third process, the composition of the iodine recovery stream is not particularly limited, although water generally constitutes the vast majority of the iodine recovery stream, for instance, at least about 60 wt. %, at least about 70 wt. %, or at least about 80 wt. %, at least about 85 wt. %, or at least about 90 wt. %, water. Iodine that is solubilized and removed from the solid fraction (which comprises the copper compound containing iodine) can be recovered in the iodine recovery stream. Any suitable amount of iodine can be present in the iodine recovery stream, but representative ranges include from about 1 to about 200 g/L iodine, from about 1 to about 50 g/L iodine, from about 2 to about 40 g/L iodine, or from about 2 to about 30 g/L iodine.

The conditions and components disclosed herein can be combined in any manner to effectuate an efficient removal of iodine from the solid fraction and into the iodine recovery stream. Generally, at least about 5 wt. % or at least about 15 wt. % of the original iodine in the solid fraction is present in the iodine recovery stream, and more often, at least about 35 wt. %, at least about 45 wt. %, at least about 55 wt. %, or at least about 65 wt. %, and in some instances, up to about 80-95 wt. %, of the original iodine from the solid fraction can be recovered in the iodine recovery stream.

Beneficially, very little copper generally is present in the iodine recovery stream, and such is unexpected given the relatively large amounts of iodine that can be present. In one aspect, for instance, the iodine recovery stream can contain less than or equal to about

1 wt. % copper. In another aspect, the iodine recovery stream can contain less than or equal to about 1000 ppm copper. Yet, in another aspect, the iodine recovery stream can contain less than or equal to about 100 ppm copper.

Referring to the first process, the iodine recovery stream can contain from about 1 to about 200 g/L, from about 1 to about 50 g/L, from about 2 to about 40 g/L, or from about

2 to about 30 g/L more iodine than that present in the pregnant leach solution prior to step (i). However, very little additional copper is present. Thus, the iodine recovery stream typically contains no more than about 1 wt. %, no more than about 1000 ppm, or no more than about 100 ppm, of copper greater than that present in the pregnant leach solution prior to step (i).

Optionally, the amount of iodine present in the solid fraction can be monitored, and the amount of the basic material or the basic solution added can be controlled accordingly. For instance, the first process, the second process, and the third process can further comprise the steps of determining (or measuring) the amount of the iodine in the solid fraction, and adjusting the amount of the basic material or the basic solution based on the amount of the iodine in the solid fraction. Thus, more or less basic material or basic solution can be added based on the amount of iodine in the solid fraction, thereby reducing waste and cost by avoiding excess addition of the basic material or basic solution, when it is not needed. Any suitable technique can be used to determine the amount of iodine in the solid fraction, one of which is to subtract the amount of iodine in the pregnant leach solution from the amount of iodine in the aqueous-based leaching solution. An illustrative and non-limiting example of a precious metal leaching process with iodine recovery is shown in FIG. 1. The process 10 shown in FIG. 1 has three main operations - preparation of a leaching solution 20, leaching of a substrate 30, and recovery of a precious metal and iodine 40. Generally, the leaching solution is an aqueous-based leaching solution containing iodine, such as described in U.S. Patent Publication No. 2017/0369967, incorporated herein by reference in its entirety. Prior to contacting with the precious metal-containing substrate, the aqueous-based leaching solution can be treated electrochemically to an oxidation-reduction potential (ORP) of at least 540 mV SHE (standard hydrogen electrode), and more often, to at least 570 mV SHE. In operation 30, the precious metal-containing substrate is contacted with the leaching solution (which contains iodine). The leaching step extracts the precious metal from the substrate, forming a pregnant leach solution containing the precious metal, and a solid fraction that contains a portion of the original solid substrate, as well as copper compounds containing iodine. In operation 40, the precious metal is recovered from the pregnant leach solution using any suitable technique. After removal of the precious metal, the barren leach solution can be reactivated chemically or electrochemically, and additional components can be added to the barren leach solution, for reuse in subsequent leaching operations. Additionally, in operation 40, the solid fraction can be treated with a basic material or basic solution in order to recover the iodine, for instance, as in the first process, the second process, and the third process disclosed herein.

EXAMPLES

The invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations to the scope of this invention. Various other aspects, embodiments, modifications, and equivalents thereof which, after reading the description herein, can suggest themselves to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

In the examples below, the starting material (a solid substrate containing the precious metal) was leached with an aqueous leaching solution containing iodine and then filtered to separate the solid fraction from the pregnant leach solution. The solid fraction was then filtered and washed using water and a solution of NaOH in different orders. In each case, a significant and unexpectedly large portion of the iodine recovery resulted from the using the high pH wash solution. Water washing only provided a small amount of iodine recovery, regardless of whether it was used in the first stage or in an intermediate stage. A Panalytical Epsilon 4 XRF unit was used to measure the iodine content in the solutions.

Example 1 - Copper bearing mineral concentrate containing 27% copper.

A sample of a mineral concentrate generated by froth flotation and gravity concentration, having a grade of 27 wt. % copper and 304 grams/ton of gold, was leached with an iodine/iodide based solution for a period of 4 hours at a pulp density of 20 wt. %. The slurry was then filtered to separate the solids from the pregnant leach solution. The solid fraction (containing copper iodide) was then washed (at 20-25°C) by passing water or a solution of sodium hydroxide through the filter cake in three stages. The duration of each wash stage was 5-10 minutes. In Example 1A, the solids were washed twice using water, followed by using a 2 M solution of sodium hydroxide (1.02 moles of hydroxide per mole of iodine). In Example IB, the solids were washed first with a 2 M solution of sodium hydroxide (3.11 moles of hydroxide per mole of iodine) followed by stages of washing only with water. The amount of iodine recovered in each stage is summarized in Table I, as well as the amount of iodine (wt. %) in the solids prior to washing. The concentration of iodine recovered in the caustic wash stream for Example 1 A and Example IB was 165 g/L and 47 g/L iodine, respectively, while the copper content was estimated to be less than 500 ppm.

Example 2 - Copper bearing ground electronic waste.

A sample of ground electronic waste (e-waste) having a grade of 25 wt. % copper was leached with an iodine/iodide based solution for a period of 1 hour at a pulp density of 25 wt. %. The slurry was then filtered to separate the solid fraction (containing copper iodide) from the pregnant leach solution. The solids were then washed washed (at 20-25°C) by passing water or a solution of sodium hydroxide through the filter cake in three stages. The duration of each wash stage was 5-10 minutes. In Example 2A, the solids were washed first with a 1 M solution of sodium hydroxide (6.3 moles of hydroxide per mole of iodine), followed by stages of washing only with water. In Example 2B and Example 2C, washing with the basic 1 M sodium hydroxide solution (5.7-5.8 moles of hydroxide per mole of iodine) was performed in the second and third wash stages, respectively. The amount of iodine recovered in each stage is summarized in Table II, as well as the amount of iodine (wt. %) in the solids prior to washing. The concentration of iodine recovered in the caustic wash stream for Example 2A, Example 2B, and Example 2C was 14.6 g/L, 10.9 g/L, and 11.7 g/L iodine, respectively, while the copper content was estimated to be less than 500 ppm. Table I - Summary of Example 1.

Table II - Summary of Example 2.

Claims

We claim: 1. A process for recovering iodine from a solid fraction comprising a copper compound containing iodine, the process comprising:

(a) contacting, in an aqueous medium, the solid fraction with a basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous medium; and (b) separating at least a portion of the aqueous medium from the solid fraction to form an iodine recovery stream.

2. The process of claim 1, wherein step (a) comprises agitating the solid fraction with the basic solution in the aqueous medium.

3. A process for recovering iodine from a solid fraction comprising a copper compound containing iodine, the process comprising:

(A) contacting the solid fraction with an aqueous basic solution having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the aqueous basic solution; and

(B) separating at least a portion of the aqueous basic solution from the solid fraction to form an iodine recovery stream.

4. The process of claim 3, wherein step (A) comprises washing the solid fraction with the aqueous basic solution, with or without agitation.

5. The process of any one of claims 1-4, wherein the iodine recovery stream contains less than or equal to about 1 wt. % copper, less than or equal to about 1000 ppm copper, or less than or equal to about 100 ppm copper.

6. The process of any one of claims 1-5, wherein the iodine recovery stream contains from about 1 to about 200 g/L iodine, or from about 2 to about 30 g/L iodine.

7. The process of any one of claims 1-6, wherein the iodine recovery stream contains at least about 70 wt. % water, at least about 80 wt. % water, or at least about 90 wt. % water.

8. A process for recovering iodine from an aqueous mixture of a solid fraction and a pregnant leach solution, wherein the solid fraction comprises a copper compound containing iodine and the pregnant leach solution comprises gold and iodine, the process comprising:

(i) contacting the mixture with a basic material having a pH of at least about 10 to solubilize at least a portion of the iodine from the solid fraction and into the pregnant leach solution, wherein the basic material comprises a basic solid and/or a basic solution; and

(ii) separating at least a portion of the pregnant leach solution from the solid fraction to form an iodine recovery stream.

9. The process of claim 8, wherein the basic material comprises the basic solution.

10. The process of claim 8, wherein the basic material comprises the basic solid, and wherein the basic solid comprises solid NaOH and/or solid KOH.

11. The process of any one of claims 8-10, wherein step (i) comprises agitating the mixture and the basic material.

12. The process of any one of claims 8-11, wherein prior to step (i), the pregnant leach solution contains from about 1 to about 10,000 mg/L of gold, or from about 1 to about 1000 mg/L of gold.

13. The process of any one of claims 8-12, wherein prior to step (i), the pregnant leach solution contains from about 1 to about 500 g/L of iodine, or from about 1 to about 100 g/L of iodine.

14. The process of any one of claims 8-13, wherein prior to step (i), the pregnant leach solution contains at least about 50 wt. % water, at least about 75 wt. % water, or at least about 90 wt. % water.

15. The process of any one of claims 8-14, wherein the pregnant leach solution further comprises palladium and/or platinum.

16. The process of any one of claims 8-15, wherein the iodine recovery stream contains from about 1 to about 200 g/L, or from about 2 to about 30 g/L, more iodine than that in the pregnant leach solution prior to step (i).

17. The process of any one of claims 8-16, wherein the iodine recovery stream contains no more than about 1 wt. %, no more than about 1000 ppm, or no more than about 100 ppm, of copper greater than that present in the pregnant leach solution prior to step (i).

18. The process of any one of the preceding claims, wherein the copper compound containing iodine comprises copper iodide.

19. The process of any one of the preceding claims, wherein the basic solution comprises LiOH, NaOH, KOH, NTUOH, or any combination thereof.

20. The process of any one of the preceding claims, wherein the basic solution has a molarity in a range from about 0.1 to about 5 M, or from about 0.5 to about 2.5 M.

21. The process of any one of the preceding claims, wherein the pH is at least about 12, at least about 13, or from about 12 to about 14.

22. The process of any one of the preceding claims, wherein the solid fraction contains from about 0.1 to about 80 wt. % copper, from about 1 to about 40 wt. % copper, or from about 0.5 to about 5 wt. % copper.

23. The process of any one of the preceding claims, wherein the solid fraction contains from about 0.1 to about 40 wt. % iodine, from about 0.1 to about 15 wt. % iodine, or from about 0.1 to about 5 wt. % iodine.

24. The process of any one of the preceding claims, wherein the solid fraction further comprises a metal selected from iron, nickel, zinc, aluminum, or any combination thereof.

25. The process of any one of the preceding claims, wherein the solid fraction further comprises a mineral selected from an elemental mineral, a silicate mineral, an oxide mineral, a sulfide mineral, a sulfate mineral, a halide mineral, a carbonate mineral, a phosphate mineral, or any combination thereof.

26. The process of any one of the preceding claims, wherein the solid fraction further comprises a plastic material.

27. The process of any one of the preceding claims, wherein excess basic material or excess basic solution is recycled.

28. The process of any one of the preceding claims, wherein a percentage amount of original iodine in the solid fraction that is present in the iodine recovery stream is at least about 5 wt. %, at least about 15 wt. %, at least about 35 wt. %, at least about 45 wt. %, or at least about 55 wt. %.

29. The process of any one of the preceding claims, wherein a molar ratio of base equivalents of the basic material or basic solution to iodine in the solid fraction is at least about 1:1.

30. The process of any one of the preceding claims, wherein a molar ratio of base equivalents of the basic material or basic solution to iodine in the solid fraction is from about 2: 1 to about 50: 1 , or from about 2: 1 to about 10:1.

31. The process of any one of the preceding claims, wherein each step is conducted, independently, at a temperature in a range from about 10 °C to about 85 °C, or from about 20 °C to about 50 °C.

32. The process of any one of the preceding claims, wherein each step is conducted, independently, at a pressure in a range from ambient to about 200 psig (1378 kPag), or from ambient to about 100 psig (689 kPag).

33. The process of any one of the preceding claims, wherein each step is conducted, independently, for a time period in a range from about 30 sec to about 24 hr, or from about 1 min to about 30 min.

34. The process of any one of the preceding claims, wherein the separating step comprises extraction, filtration, evaporation, distillation, draining, pressing, centrifuging, or any combination thereof.

35. The process of any one of the preceding claims, wherein the process comprises at least two contacting steps and at least two separating steps, performed in any order.

36. The process of any one of the preceding claims, wherein prior to step (i), step (a), or step (A), further comprising the step of contacting a solid substrate comprising a precious metal with an aqueous-based leaching solution containing iodine to form the pregnant leach solution and the solid fraction.

37. The process of claim 36, further comprising a step of separating at least a portion of the solid fraction from the pregnant leach solution.

38. The process of any one of the preceding claims, further comprising the steps of: determining an amount of the iodine in the solid fraction; and adjusting an amount of the basic material or the basic solution based on the amount of the iodine in the solid fraction.

39. The process of claim 38, wherein the amount of the iodine is determined by the subtracting the amount of iodine in the pregnant leach solution from the amount of iodine in the aqueous-based leaching solution.