TITLE OF THE INVENTION

A SELECTIVE AND EFFICIENT PROCESS FOR THE EXTRACTION OF NOBLE METAL IONS FROM COMPLEX MIXTURES

FIELD OF THE INVENTION

The present invention relates to the use of an affordable, selective, and sustainable medium for the industrial extraction of noble metals from a solution containing multiple ions using sustainable composite materials.

BACKGROUND OF THE INVENTION

Industrial extraction of gold (Au) and other precious noble metals causes a significant environmental impact due to the use of hazardous chemicals such as cyanide, mercury, and acids. Enhancing sustainability by reducing the use of these materials and new process is important in ensuring a safe planet. While there have been many methods introduced in the recent past, extraction with the biomolecule niacin for selective extraction of gold ions gained significant attention [ACS Sustain. Chem. Eng.2021, 9, 2129]. This process has been patented in the recent past [IN202041047984]. However, the use of these technologies industrially would involve the development of appropriate processes so that the chemistry can be utilized economically.

Noble metals are resistant to chemical corrosion. Extraction of noble metals from minerals and their subsequent processing requires highly reactive conditions and toxic chemicals [Environ. Sci. Technol.2005, 39, 4655]. All of the known noble metal extraction processes used in industries are environmentally hazardous due to the use of highly toxic chemicals, which contribute to water and soil pollution. Several methods have been reported earlier for the extraction of different noble metals such as gold (Au), palladium(Pd), silver(Ag), platinum (Pt), etc.[Sci. Rep.2018, 8, 16909; Hydrometallurgy2020, 191, 105241]. It is necessary to have a green and efficient method to extract noble metals. Direct extraction of metal into a solution requires strong interaction of the metal with specific molecules. This is often done with ions such as cyanide, which form strong complexes with noble metals. Different biomolecules such as lipids, carbohydrates, and proteins form weak non-covalent complexes with several metals[Eur. J. Inorg. Chem.2017, 2017, 3072]. Square -planar tetrahaloaurate anions ([AUX4]-, X = Cl/Br) form inclusion complexes with and y-CDs [Adv. Funct. Mater.2010, 20, 951], The strong affinity with different functional groups, such as -COOH, -NH2, -SH, -OH, etc., towards metals, including silver and gold, has attracted researchers to create novel nano-biocomposites involving such functionalities [NPG Asia Mater.2013, 5, e39; J. Am. Chem. Soc.2016, 138, 11643]. However, such interactions are weak and, therefore, are rarely used for extraction. Injection of metals into the biological system as ions/complexes has also been reported, where small nanoparticles were synthesized in-vivo, within the bacterial cells, following the biomineralization pathwayfj. Am. Chem. Soc.2016, 138, 11643]. Electrochemical dissolution of noble metals is an important step in extracting, refining, and processing metals [Angew. Chem. Int. Ed. Engl.2011, 50, 6346; ChemCatChem2014, 6, 2219; Nat. Commun.2016, 7, 1]

Typically, extraction of noble metal involves various chemical or electrochemical methods [Environ. Sci. Technol.2005, 39, 4655]. Matthew M. Matlock et al. demonstrated the removal of heavy metals from wastewater derived from the lead battery industry by a chemical precipitation method [Ind. Eng. Chem. Res.2002, 41, 5278]. Because of the slow-leaching rates of silver, G. Deschenes et al. used a high concentration of cyanide to maximize the leaching of silver from high-grade ore samples [Mining, Metall. Explor.2011, 28, 37]. T. Ogata reported a novel recovery system for gold, one of the precious metals in electronic scrap, utilizing tannin gel particles. The adsorption mechanism of gold onto tannin gel particles was also elucidated. The adsorption of gold occurs through the reduction of trivalent gold ions to metallic gold on the surface of tannin gel particles, which is accompanied by simultaneous oxidization of the hydroxyl groups of tannin gel [Water Res.2005, 39, 4281]. Yong Guo et al. demonstrated a photoreduction strategy for selective recovery of gold by carbon nitride[J. Mater. Chem. A2014, 2, 19594]. Z. Liu et al. reported spontaneous assembly of a one-dimensional supramolecular complex with an extended {[K(OH2)e][AuBr4] cz (a-cyclodextrin)2] _n chain superstructure, formed during rapid co-precipitation of KAuBr4 and oc -cyclodextrin in water. The phase change is selective for this gold salt, even in presence of other square -planar palladium and platinum complexes[Nat. Commun.2013, 4].

Manabu Yamada et al. reported rapid and selective recovery of palladium (Pd) using a thioamide-modified calix [4] arene adsorbent. Chen Zhou et al. reported palladium recovery in an H2~ based membrane biofilm reactor [Environ. Sci. Technol.2016, 50, 2546]. Damien bourgeoiset al. reported a process for removal of Pd from printed circuit boards(PCB).Awual et al. reported a ligand-based approach using 5-tert-butyl-2-hydroxybenzaldehyde thiosemicarbazone for efficient palladium(Pd(II)) separation and recovery [Sensors Actuators B Chem.2015, 209, 790]. Baksi et al. reported the selective extraction of silver (Ag) into solution from the bulk metal, by carbohydrates, mainly glucose[Angew. Chemie Int. Ed.2016, 55, 7777]. Youssef Chehade reported recovery of Au, Pd, Ag, etc., from waste PCB.

Globally, the gold extraction is performed by the cyanide method. Typically, this involves chemical and electrochemical methods. The extraction process typically followed by the mining industry is cyanidation, which contributes to water and soil pollution [Geotech. Geol. Eng.2006, 24, 1545]. Generally, a noble metal complex mixture has a large amount of other metals ions. Also, electronic waste or industrial waste has other metals in huge concentrations compared to the noble metal. Thus, it is necessary to develop a green and efficient method to selectively extract different noble metals (i.e., Au, Pd, Ag, etc.). We believe that our recently discovered soft chemistry approach can be efficiently used for different noble metals in industrial conditions. Our methodology and process are very simple, cost-effective, and constitute a green technology for the mining industry.

Globally, the metal extraction process is performed using cyanide, which forms strong complexes with noble metals. However, the use of cyanide during the extraction process can lead to water and soil pollution. Thus the present invention provides a simple and green methodology for extraction of noble metals from ores, using a soft chemistry approach. Selective metal extraction from ores requires strong interaction of the metal with specific molecules, leading to the formation of metal complexes in the solution. These complexes can be further reduced to extract the metal.

OBJECT OF THE INVENTION

An object of the present invention is to a simple and green methodology for extraction of noble metals from ores, using a soft chemistry approach. Selective metal extraction from ores requires strong interaction of the metal with specific molecules, leading to the formation of metal complexes in the solution. These complexes can be further reduced to extract the metal.

An object of the present invention is to provide a highly cost-effective and sustainable method of gold extraction in which aqueous Au ³⁺ is precipitated selectively as it’ s complex with niacin-incorporated polystyrene, with a formula [AuC14]’[2Niacin+H] ⁺ -PS. SUMMARY OF THE INVENTION

The present invention relates to a selective and efficient process for the extraction of noble metal ions from complex mixtures using a sustainable composite materials.

In one embodiment, the present invention relates a simple and green methodology for extraction of noble metals from ores, using a soft chemistry approach. Selective metal extraction from ores requires strong interaction of the metal with specific molecules, leading to the formation of metal complexes in the solution.

In one embodiment, the present invention provide a highly cost-effective and sustainable method of gold extraction in which aqueous Au ³⁺ is precipitated selectively as it’ s complex with niacin-incorporated polystyrene, with a formula [AuC14]’[2Niacin+H] ⁺ -PS abbreviated as complex C, from its mixtures with Be ²⁺ , Ba ²⁺ , Sr ²⁺ ’ Ti ³⁺ , V ³⁺ , Cr ³⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ ,Cd ²⁺ , Pb ²⁺ , AS ^+3/5 , Sb ³⁺ , Se ²⁺ , Sn ²⁺ , Tl ⁺ , Fe ³⁺ , Pt ²⁺ , and Zn ²⁺ , along with common ions such as alkali (Na ⁺ /K ⁺ ), alkaline earth (Mg ²⁺ /Ca ²⁺ ) metal ions and Al ³⁺ .This method was also employed to extract other noble metals such as Pd, Ag, and Pt from the mixture of other reactive metal ions mixture (such as Au ³⁺ , Pd ²⁺ , Rh ³⁺ , Ru ³⁺ , Ag ⁺ , Hf ⁴⁺ , Ir ⁴⁺ , Te ²⁺ , Pt ²⁺ , etc.). The present invention observed that the noble metal ions could be extracted by the PS -niacin composite (composite X). The said material is very much effective for harsh industrial conditions such as pH 1 to 3. Niacin and styrene, being inexpensive, the method may be used for affordable, selective, and sustainable extraction of precious noble metals from diverse raw materials.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 depicts a schematic representation of the synthesis of niacin-incorporated polystyrene (optimized composite X)

Figure 2 shows FT-IR of PS, niacin, and PS-niacin composite.

Figure 3 A) Au ³⁺ adsorption study using optimized PS-niacin composite X; B) is the expanded view of A.

Figure 4 shows pH-dependent study using optimized composite X after 24 h of adsorption with 1 ppm Au ³⁺ solution.

Figure 5 Time-dependent adsorption study at pH 1.05 using optimized composite X (100 mg in 100 ml Au solution). Figure 6 Regeneration study of Au A) saturated and B) unsaturated adsorbent (composite X) using regenerated solutions.

Figure 7 Effect of adsorption of composite X with various ions.

Figure 8 shows selective adsorption of different noble metals from a mixture with different input concentrations.

Referring to the drawings, the embodiments of the present invention are further described. The figures are not necessarily drawn to scale, and in some instances, the drawings have been exaggerated or simplified for illustrative purposes only. One of the ordinary skills in the art may appreciate the many possible applications and variations of the present invention based on the following examples of possible embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features disclosed herein.

The present invention relates to a selective and efficient process for the extraction of noble metal ions from complex mixtures using a sustainable composite materials.

The present invention relates a simple and green methodology for extraction of noble metals from ores, using a soft chemistry approach. Selective metal extraction from ores requires strong interaction of the metal with specific molecules, leading to the formation of metal complexes in the solution.

The present invention provide a highly cost-effective and sustainable method of gold extraction in which aqueous Au ³⁺ is precipitated selectively as it’s complex with niacin- incorporated polystyrene, with a formula [AuC14]’[2Niacin+H] ⁺ -PS abbreviated as complex C, from its mixtures with Be ²⁺ , Ba ²⁺ , Sr ²⁺ ’ Ti ³⁺ , V ³⁺ , Cr ³⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ ,Cd ²⁺ , Pb ²⁺ , AS ^+3/5 , Sb ³⁺ , Se ²⁺ , Sn ²⁺ , Tl ⁺ , Fe ³⁺ , Pt ²⁺ , and Zn ²⁺ , along with common ions such as alkali (Na ⁺ /K ⁺ ), alkaline earth (Mg ²⁺ /Ca ²⁺ ) metal ions and Al ³⁺ .This method was also employed to extract other noble metals such as Pd, Ag, and Pt from the mixture of other reactive metal ions mixture (such as Au ³⁺ , Pd ²⁺ , Rh ³⁺ , Ru ³⁺ , Ag ⁺ , Hf ⁺ , Ir ⁴⁺ , Te ²⁺ , Pt ²⁺ , etc.). The present invention observed that the noble metal ions could be extracted by the PS-niacin composite (composite X). The said material is very much effective for harsh industrial conditions such as pH 1 to 3. Niacin and styrene, being inexpensive, the method may be used for affordable, selective, and sustainable extraction of precious noble metals from diverse raw materials.

The present invention relates to the development of a selective, affordable and sustainable media for industrial Au extraction. Figure 1 depicts the schematic representation of the synthesis of niacin-incorporated polystyrene. Reaction of styrene monomer with niacin at 90 °C with the presence of potassium persulfate (K2S2O8) and surfactant sodium dodecyl sulphate (SDS)in the in situ polymerization process produces niacin-incorporated polystyrene where the active -group of niacin is available for selective Au uptake.

Figure 2 (Ai-Aiii) illustrates FT-IR comparison features of PS, niacin, and PS-niacin composite. Characteristic peak -3300-3550 cm’ ¹ was observed in Figure 2 (i-iii) due to the O-H frequency of or N-H frequency of the materials. The characteristic peak around 3025 cm’ ¹ for the C-H aromatic bond, peaks at 2920 and 2849 cm’ ¹ due to aliphatic C-H are observable. Two new peaks at~1636 and -1193 cm ^-1 were observed for the PS-niacin composite, which is due to C-H and N-H bonds, indicating an interaction between PS and niacin. Therefore, bond formation between PS and niacin was proven. The presence of both niacin and PS features in the spectra indicates the formation of the niacin-PS composite in Figure 2 iii.

Figure 3 (A and B) illustrates an adsorption study using optimized PS-niacin composite X with lower and higher Au ³⁺ concentrations. In both cases, observed high adsorption capacity - 98.6% and -99.7% for higher and lower concentrations of input Au solution, respectively.

Figure 4 illustrates a pH-dependent study using the optimized composite X after 24 h of adsorption with 1 ppm Au solution. This study reveals that composite X is very efficient in all the pH (1 to 6.2) shown in the figure.

Figure 5 illustrates the time-dependent adsorption study at pH 1.05 using optimized composite X. This study has proven that for equilibrium Au adsorption (-99.2 %), time needed is approximately 2-3 h.

Figure 6 illustrates the regeneration of the adsorbed Au from material X. Au recovered from saturated and unsaturated composite X were found to be -93.55% and 51.89%, respectively. This invention revealed that the composite X will easily regenerate the surface by a regenerate solution such as sodium metabisulfite (Na2S20s), thiourea (CH4N2S), and different acids. Also, these materials could be used for further adsorption of Au cycles.

Figure 7 illustrates the effect of adsorption of composite X with various ions, which shows that noble metal ions could be extracted selectively from a complex mixture. There is no effect of other ions on noble metal extraction.

Figure 8 illustrates selective adsorption of various noble metals from a mixture with different input concentrations, which shows one could tunably extract selective noble metals from its mixture.

The results presented above demonstrate the preparation and utilization of niacin- incorporated polystyrene for industrial applications. Chemical analysis of the mining sample before and after niacin-incorporated PS (composite X) treatment is presented in Table 1. This shows 99.5 % of Au ³⁺ removal, and the concentration of other elements is unaffected. This happened at industrial relevance pH conditions such as pH 1 to 3. This selectivity adds another advantage to the process wherein precious noble metals recovered from diverse raw materials, could be left undisturbed for subsequent processes. Also, Table 2 revealed that even 10, 100, and 1000 times lesser concentrations of gold could be selectively extracted from its complex mixture with different ions such as Na ⁺ , Mg ²⁺ , Ca ²⁺ , Al ³⁺ , SiCh ² ’, Fe ²⁺ , Cl’, F’ ions, etc.) at pH 1.05. Tablel Au ³⁺ adsorption data before and after reaction with niacin-incorporated PS materials and ICP-MS data.

Table 2 Adsorption study of composite X in a 5 mL mixture (where Au=gold and M= mixture of multi-ions used such as Na ⁺ , Mg ²⁺ , Ca ²⁺ , Al ³⁺ , SiC>3 ² ’, Fe ²⁺ , Cl’, F", etc.) at pH 1.05. The stability of the polymeric system under such harsh conditions is important for industrial applications. The present invention used polystyrene in this process to make it economical. Other polymers such as polysulphone (PSf), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyaniline (PANI), polyacrylic acid (PAA)and polyacrylamide (PAM)can also be used as matrices for this process. However, the environmental sustainability of the materials has to be accessed suitably. The composite mixture of the present invention selectively removes the noble metals along with matrices including activated carbon, different graphenic materials, chitosan, cellulose materials and also used in the form of filtration column and filtration vessel. The present invention can be used in conjunction with other technology for metal extraction and with a selective electrolyzer electrode system for different noble metals extraction. The present invention can be used in various places such as industries relevant to noble metal extraction plants, mining waste, electronic waste, waste water treatment plants.

It may be appreciated by those skilled in the art that the drawings, examples and detailed description herein are to be regarded in an illustrative rather than a restrictive manner.