Description:[0001] The present disclosure pertains to a method for converting waste to valuable resource. In particular, the present disclosure pertains to electronic waste (e-waste) management and still more particularly to a sustainable method for refining tin from e-waste. The method of the present disclosure results in significant enhancement in the purity of the extracted tin, efficiency, and environmental sustainability making it an eco-friendly alternative to conventional methods.

BACKGROUND
[0002] Tin is widely used in the electronics industry, primarily as a component of solder alloys in printed circuit boards (PCBs) and electronic interconnects. The increasing volume of obsolete electronics has led to the accumulation of significant quantities of tin-containing waste, making its recovery both economically and environmentally critical.

[0003] The refinement of tin from e-waste is of high importance. First, tin is a finite natural resource, and its primary extraction through mining is associated with considerable environmental degradation, including deforestation, soil erosion, and water pollution. Therefore, recovering tin from secondary sources such as e-waste helps conserve natural resources and reduces the ecological footprint of tin production. Also, the demand for tin is rising due to its applications not only in electronics, but also in packaging, alloys, and increasingly in renewable energy technologies. Meeting this growing demand through sustainable recycling methods can enhance material security.

[0004] The existing processes for tin recovery from e-waste primarily involve energy-intensive pyrometallurgical treatments or use of hazardous chemicals in hydrometallurgical operations. These conventional methods typically yield tin with purity levels ranging between 95% and 98%, which are often insufficient for industrial-grade applications. Further, these conventional approaches present significant environmental and safety concerns, including greenhouse gas emissions, toxic waste generation, and occupational hazards.

[0005] Furthermore, tin recovered from e-waste is frequently contaminated with other metals such as lead, copper, silver, and antimony. The presence of these impurities complicates the refining process, often requiring multiple purification steps that increase cost and environmental impact. The development and implementation of sustainable e-waste processing technologies face significant challenges, particularly due to the complexity of e-waste composition and the relatively limited industrial experience and knowledge in handling these materials compared to more conventional and well-characterized industrial waste streams. This includes limited expertise in the selective recovery and purification of materials such as tin, rare earth elements, and other low-concentration yet critical metals from heterogeneous waste matrices.

[0006] Therefore, there is a pressing need for improved refining methods that can achieve higher purity, greater efficiency, and/or enhanced environmental sustainability in the recovery of tin from e-waste. The present invention addresses these challenges by providing a method that significantly improves the purity, efficiency, and ecological performance of tin recovery from e-waste.

SUMMARY OF THE DISCLOSURE
[0007] This summary is intended to introduce, in simplified form, a selection of concepts that are further described in the detailed description. This summary is merely presented as a brief overview of the subject matter described and claimed herein and does not aid in determining the scope of the claimed subject matter.

[0008] In one aspect, the present disclosure provides a method for refining tin from e-waste using an integrated method involving multiple stages under milder mechanical, chemical and thermal conditions to provide pure tin using an environmentally benign and economically viable alternative refining method.

[0009] In an aspect, the present disclosure provides a method for refining tin from impure electronic waste (e-waste) scrap, comprising:
a) pre-treating e-waste scrap by subjecting e-waste to mechanical processing and optionally thermal treatment to remove impurities and undesirable materials and obtain tin-rich pre-treated metallic scrap;
b) subjecting the pre-treated metallic scrap obtained in step a) to a controlled refining process comprising vacuum distillation and chemical purification to obtain refined tin; and
c) subjecting the refined tin to a post-processing step comprising zone-refining using a spiral zone refiner or a linear crystallizer having a rotating induction heating coil to obtain tin with enhanced purity.

[0010] In a specific aspect, the method comprises:
a) granulating or shredding e-waste scrap to smaller particles (particulates) of e-waste;
b) subjecting the e-waste particulates obtained in step a) to magnetic separation, density-based separation, and separation in an eddy current separator;
c) optionally, subjecting the tin obtained in step b) to a thermal treatment at a temperature of about 300-400 °C;
d) subjecting the thermally treated tin obtained in step c) to vacuum distillation;
e) subjecting the tin obtained in step d) to chemical purification using a fluxing agent; and
f) subjecting the tin obtained in step e) to zone refining or linear crystallizing.

In another embodiment, the present disclosure provides tin obtained from the method of the present disclosure.

[0011] BRIEF DESCRIPTION OF FIGURES
Figure 1 illustrates comparative analysis of purity, yield, energy consumption, environmental impact, and cost per kg of tin obtained using method of the present disclosure vs. pyrometallurgical, and hydrometallurgical processes known in the art.

DETAILED DESCRIPTION
[0012] The objective of the present disclosure is to arrive at a sustainable eco-friendly method for refining tin from e-waste. The method of the present disclosure is an eco-friendly process for refining tin from e-waste, offering enhanced purity, improved efficiency, and reduced environmental impact compared to conventional techniques.

[0013] The present disclosure can be understood more readily by reference to the following description, taken in conjunction with the accompanying Figures and Examples, all of which form a part of this disclosure. At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.

[0014] Before the present disclosure or methods of the present disclosure are described in greater detail, it is to be understood that the specific products, methods, processes, conditions, or parameters, are not limited to embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing embodiments only and is not intended to be limiting.

[0015] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the methods. Where the stated range includes one or both limits, ranges excluding either or both of those included limits are also included in the methods. Certain ranges are presented herein with numerical values being preceded by the term “about.” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. For example, "about" can mean within one or more standard deviations, or within ± 30%, 25%, 20%, 15%, 10% or 5% of the stated value.

[0016] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are described. For the purposes of the present invention, the following terms are defined below.

[0017] It is appreciated that certain features of the methods, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the methods, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. All combinations of the embodiments are specifically embraced by the present invention and are disclosed herein just as if each and every combination was individually and explicitly disclosed, to the extent that such combinations embrace operable processes and/or composites/scaffolds.

[0018] The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element. As used herein, the term "comprises", "comprising", or “comprising of” is generally used in the sense of include, that is to say permitting the presence of one or more features or components. The term "comprises", "comprising", or “comprising of” when placed before the recitation of steps in a process or method means that the process or method encompasses one or more steps that are additional to those expressly recited, and that the additional one or more steps may be performed before, between, and/or after the recited steps.

[0019] Reference throughout this specification to “certain embodiments”, “further embodiments”, “specific embodiments”, “further specific embodiment”, “one embodiment”, “a non-limiting embodiment”, “an exemplary embodiment”, “some instances”, or “further instances”, means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. As used herein, the terms ‘include’, ‘have’, ‘comprise’, ‘contain’ etc. or any form of said terms such as ‘having’, ‘including’, ‘containing’, ‘comprising’ or ‘comprises’ are inclusive and will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0020] The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illustrate the disclosure and does not pose a limitation on the scope of the disclosure otherwise claimed. As used herein, the term “invention”, “present invention”, “disclosure” or “present disclosure” as used herein is a non-limiting term and is not intended to refer to any single embodiment of the particular invention but encompasses all possible embodiments as described in the specification. The terms “process(es)” and “method(s)” are considered interchangeable within this disclosure.

[0021] The term "electronic waste" or "e-waste" as used herein refers to any discarded electrical or electronic devices or components thereof that are no longer in use, are obsolete, broken, or unwanted. This includes, but is not limited to, consumer electronics (such as mobile phones, computers, televisions, and audio equipment), industrial electronic equipment, batteries, circuit boards, and any associated hardware that contains electronic components. E-waste may contain a combination of reusable, recyclable, and hazardous materials.

[0022] In one aspect, the present disclosure provides a sustainable method for refining tin from e-waste. The process is an integrated process involving multiple stages of purification under milder chemical and thermal conditions to provide an environmentally benign and economically viable alternative.

[0023] From a sustainability perspective, integrated methods are generally preferred over isolated methods that involve harsh chemical or thermal conditions. The process of the present disclosure comprises a combination of techniques selected from mechanical separation, low-temperature thermal treatment, vacuum distillation, chemical purification, zone refining, and crystallization, each tailored to effectively remove impurities and isolate high-purity tin from electronic waste (e-waste) streams.

[0024] The application of milder processing conditions within the integrated framework significantly reduces the risk of toxic emissions, limits degradation of valuable co-materials, and minimizes the generation of hazardous by-products. Moreover, such integrated methods provide enhanced selectivity in separating tin from other commonly co-existing metals in e-waste, such as lead, copper, antimony, and silver, thereby improving both the purity and yield of the recovered tin product.

[0025] In an embodiment, the present disclosure provides a method for refining tin from impure electronic waste (e-waste) scrap, comprising:
a) pre-treating e-waste scrap by subjecting e-waste to mechanical processing and optionally thermal treatment to remove impurities and undesirable materials and obtain tin-rich pre-treated metallic scrap;
b) subjecting the pre-treated metallic scrap obtained in step a) to a controlled refining process comprising vacuum distillation and chemical purification to obtain refined tin; and
c) subjecting the refined tin to a post-processing step comprising zone-refining using a spiral zone refiner or a linear crystallizer having a rotating induction heating coil to obtain tin with enhanced purity.

[0026] The pre-treatment step involves selective separation of tin-bearing materials from bulk electronic waste (e-waste). This step involves mechanical, physical, or manual sorting techniques designed to isolate components known to contain tin or tin-based alloys.

[0027] The pre-treatment involves granulating or shredding the e waste using methods selected from but not limited to mechanical granulation, shredding, hammer milling, or ball milling, grinding and the like. The e-waste is mechanically shredded into particulate matter ranging in size from about 1-10 mm or from about 1-5 mm, which is an optimal range for downstream separation processes.

[0028] In a specific embodiment, granulation is carried out using a mechanical granulator. The e-waste material comprising printed circuit boards (PCBs), connectors, cables, or other electronic components can be fed into hopper of a mechanical granulator by manual or automated feeding via a conveyor system. The material is subjected to mechanical impact and shear forces generated by rotating knives or hammers against a fixed cutting surface or screen. The granulator can be a single-shaft shredder or a twin-shaft rotary shear, or hammer mill. The rotor speed of the granulator can be maintained at about 600-1500 rpm, and the screen size of the fixed cutting surface or screen can range from 2-20 mm, or from about 2-10 mm. The size of the output material can be controlled at about 1-10 mm, or to about 1-5 mm depending on the requirements.

[0029] The granulated material can be suitably discharged onto a vibrating screen or air classifier to separate into different size fractions optimized for subsequent processing.

[0030] Following granulation, the particulate stream is subjected to magnetic separation to remove ferrous contaminants such as steel fragments, screws, and iron-based alloys. A high-intensity permanent magnet or electromagnet can be used to divert magnetic particles away from the tin-rich fraction. Magnetic field strength can be maintained at about 0.5-3.0 tesla, or from about 0.5-2.0 tesla. When the separation is carried out in magnetic drum, the drum speed can be maintained at 10-100 rpm, or from 20-60 rpm, and when the separation is carried out on a belt, the separator gap can be maintained at about 1-10 mm, or from about 1-5 mm. Principally, the magnetic separation focuses on recovery of iron and steel.

[0031] Subsequently, the non-ferrous material undergoes density-based separation, which can be performed using an air classifier or vibrating table. In this separation process, particles move down a sloped, vibrating table with a fluid which can be air or water. The table slope is suitably maintained at about 3-7°, and the vibration speed is maintained at about 300-600 rpm. Heavier particles stratify and settle closer to the table’s surface, while lighter materials move toward the top and are washed off. Tin and lead, having relatively high specific gravities settle in specific zones of the separator, facilitating their collection.

[0032] To further refine the stream and eliminate non-conductive, non-metallic components such as plastics, fiberglass, and ceramic substrates, the processed material is passed through an eddy current separator. Tin-rich particles exhibit sufficient electrical conductivity to respond to eddy currents generated in high-speed rotating magnetic fields. Unlike magnetic separation, eddy current separation is suited for non-ferrous conductive metals like tin, aluminum, and copper. This device induces eddy currents in conductive particles, generating a repulsive magnetic field that causes them to be deflected away from non-conductive materials. The result is an enriched fraction of metallic tin-bearing particles, substantially free of unwanted substrate materials.

[0033] The eddy current separator suitably comprises a high-speed rotating motor, housed within a non-conductive drum. As the conductive granules pass over the rotor, eddy currents are induced in conductive particles, creating opposing magnetic fields that eject them from the stream. The drum speed can range from about 2000 to 4000 rpm, or from about 2000 to 3000 rpm.

[0034] This mechanically integrated separation sequence improves process efficiency and ensures that subsequent thermal or chemical purification steps operate on a pre-concentrated, contaminant-reduced feedstock, thereby reducing energy consumption and reagent use in the overall recovery process.

[0035] The separated tin-bearing fraction may optionally be subjected to a thermal pre-treatment, carried out under controlled temperature conditions, to facilitate the removal of volatile organic compounds, moisture, and loosely bound organic and plastic residues.

[0036] The thermal pre-treatment can be performed using indirect heating equipment, such as a rotary kiln or a sealed chamber furnace, which allows for controlled thermal exposure without direct flame contact. The system is operated under an inert or mildly reducing atmosphere, typically using nitrogen (N2), carbon dioxide (CO2), or a mixture thereof, to prevent oxidation of tin and other valuable metals.

[0037] The temperature is maintained in the range of about 200-500 °C or from about 300°C to 400°C, and the residence time is between about 10 to 80 minutes to about 30 to 60 minutes, depending on the composition and thickness of the feedstock material. In an embodiment, the thermal treatment is carried out at about 350 °C for about 45 minutes in a rotary kiln under nitrogen atmosphere.

[0038] This additional pre-treatment step enhances the effectiveness of downstream vacuum distillation or chemical purification, by reducing slag formation, improving metal recovery efficiency, and extending the life of refining equipment. Additionally, it contributes to sustainability of the process by minimizing the generation of hazardous by-products and allowing for cleaner, more selective separation of tin in the subsequent refining stages.

[0039] Step b) involves subjecting the pre-treated metallic scrap obtained in step a) to a controlled refining process comprising vacuum distillation. This step is employed to selectively separate tin from lower-boiling-point contaminants. In this step, the material is heated under reduced pressure conditions to selectively volatilize and remove lower-boiling-point contaminants, such as residual organic compounds, lead, and zinc. Tin, having a higher boiling point, remains predominantly in the condensed phase. Subsequent to vacuum distillation, the partially purified tin may be subjected to chemical purification using selective fluxing agents for removal of residual metallic impurities by forming immiscible slag phases or volatile complexes, which can be separated by decanting or filtration.

[0040] Vacuum distillation is suitably carried out at temperature range of about 400 to 800 °C or from about 500-700 °C under a vacuum of about 0.01 to 0.1 mm/Hg or from about 0.05 mm/Hg.

[0041] The process is carried out in a vacuum distillation unit (VDU) comprising a sealed heating chamber equipped with a graphite or ceramic crucible for holding the scrap feed. The VDU also includes a condenser system to capture volatilized impurities and an off-gas handling system to safely treat any gaseous by-products generated during distillation. Under the reduced pressure environment, contaminants such as lead (Pb), cadmium (Cd), and arsenic (As) volatilize or undergo oxidation preferentially, owing to their lower boiling points or higher vapor pressures compared to tin.

[0042] The vaporized impurities flow into a condenser or cold trap system, where they encounter cooled surfaces maintained at temperatures low enough to cause the vapors to condense into liquid or solid form. Cooling is typically achieved by circulating chilled fluids (water, glycol) or cryogenic coolants. The condensed impurities accumulate in a dedicated collection reservoir or trap, physically separated from the vacuum chamber. This prevents contamination of the purified tin and allows for safe handling and disposal or recovery of these separated metals.

[0043] In a specific embodiment, vacuum distillation is carried out in a vacuum distillation unit at a temperature of about 600 °C, at a pressure of 0.05 mmHg, for a duration of 2 hours.

[0044] Followed by vacuum distillation, the purified tin is subjected to chemical purification. Chemical purification is aimed at selectively binding and removing residual trace metal impurities such as iron (Fe), antimony (Sb), zinc (Zn), copper (Cu) and arsenic (As). The chemical purification comprises adding a fluxing agent to the pre-treated metallic scrap in molten state simultaneously with or subsequent to the vacuum distillation; wherein the fluxing agent is capable of binding with metal impurities present in the molten material. In certain embodiments, the fluxing agent is capable of binding with arsenic, copper, and/or iron. In some embodiments, the fluxing agent is chloride salt.

[0045] Selective fluxing agents are selected from chloride salts selected from, but not limited to ZnCl2, NH4Cl, NaCl, KCl, and combinations thereof. In some embodiments, the fluxing agent is a mixture of ZnCl2 and NH4Cl.

[0046] In a specific embodiment, the chemical purification is carried out in a presence of a combination of ZnCl2-NH4Cl at a ratio of 1:1, and the fluxing agents are capable of binding with arsenic, copper, and iron.

[0047] The fluxing agents are used in quantities of about 1-10 wt%, or from about 2-8 wt% to the total weight of the tin to be purified. and may optionally be combined with proprietary scavenger compounds specifically formulated to bind arsenic and iron impurities selected from arsenic scavengers such as sodium nitrate, potassium permanganate, calcium hydroxide calcium carbonate, magnesium/aluminum oxides; and iron scavengers such as sodium meta phosphates, alkali metal chlorides titanium oxide and the like or their mixtures.

[0048] Chemical purification can be performed on molten tin under an inert atmosphere, such as argon (Ar) or nitrogen (N2), to prevent oxidation and contamination. The fluxing agents can be carefully added to the molten tin bath at controlled temperatures, ensuring thorough mixing and reaction with impurity species. The trace metals form stable slag phases or metal-flux complexes that exhibit lower density and immiscibility with the molten tin matrix. The slag layer, enriched with bound impurities can be physically removed by skimming.

[0049] This chemical purification step provides a mild, efficient, and selective method to reduce impurities without harsh chemical reagents or complex downstream treatments. When combined with prior vacuum distillation and subsequent zone refining, it ensures the production of tin with purity levels suitable for high-value applications. The process excludes the use of strong acids, cyanides, or other highly corrosive chemicals, thereby enhancing safety and environmental compatibility.

[0050] Step c) comprises zone refining of the partially purified tin to achieve ultra-high purity. This step is particularly effective for removing trace-level metallic impurities based on differential solubility and segregation coefficients during directional solidification. The process utilizes a spiral zone refiner and/or a linear crystallizer equipped with a rotating induction heating coil. This step enables the removal of trace metals such as lead, bismuth, antimony, and silver, which are otherwise difficult to eliminate through conventional chemical or thermal methods.

[0051] The zone refining apparatus comprises a heating coil that generates an induction field, melting a narrow zone of the tin ingot or feedstock. The coil either mechanically moves along a spiral track or is positioned on a magnetically driven turntable, imparting a spiral motion to the molten zone. This spiral movement promotes uniform heating and directional solidification progressing from the core toward the periphery of the ingot. The design ensures precise control over the molten zone’s position and movement, facilitating continuous purification as the molten zone traverses the tin mass.

[0052] The tin is cast into a cylindrical or conical ingot and positioned within a zone refining apparatus comprising a rotating induction heating coil which is the heating element and a mechanically or magnetically actuated turntable that imparts a spiral motion to the tin ingot relative to the spiral induction heating coil. This spiral motion ensures enhanced mixing within the molten zone and promotes uniform redistribution of impurities toward the tail end of the refining direction.

[0053] The spiral movement of the tin material is achieved either by a mechanical indexing platform that rotates and linearly translates the ingot beneath the induction coil; or a magnetically driven turntable system. This movement ensures that the molten zone created by the induction heater traverses the ingot surface along a spiral path. The zone refining process is carried out under a controlled inert atmosphere, such as nitrogen (N2) or argon (Ar), to prevent oxidation of tin and to ensure thermal stability of the melt interface.

[0054] Temperature in the spiral zone refiner can be maintained between about 200 to about 600 °C or from about 350 °C and about 450°C along the spiral path, optimized to sustain a narrow molten zone and promote steady solidification. The temperature at the hot end is maintained at about 400 °C, and the temperature at the cool end is maintained at about 200 °C.

[0055] The induction coil traverses the length of the tin mass at a controlled rate of about 0.5 mm/min to 5 mm/min, depending on the desired purification level, regulated by the speed of the rotating coil and the cooling system, to allow sufficient time for impurities to migrate. This slow passage ensures the establishment of a narrow molten zone which migrates progressively along the ingot, carrying less soluble impurities toward the trailing edge due to their unfavorable partition coefficients.

[0056] Impurities with different solubility and segregation coefficients migrate towards the melting zone, concentrating in the liquid phase. The tin crystallizes cleanly behind the molten zone, leaving impurities concentrated in the remaining molten portion. This impurity-enriched molten zone moves towards the tail end of the ingot, where it can be removed as a purified residue.

[0057] To achieve the desired purity the zone refining step is repeated for two or more full cycles, wherein each cycle involves a full pass of the molten zone from one end of the ingot to the other. After completion of each cycle, the ingot may be repositioned or rotated in reverse to alternate the direction of refining for improved efficiency. In a specific embodiment, two to three passes of the zone refining process are performed to achieve ultra-high-purity tin ingots with purity levels exceeding 99.90% by weight.

[0058] In a specific embodiment, the e-waste is solder scrapcontaining about 60% Sn, about 38% Pb, about 1% Cu/Fe, about 1% others. The disclosed method enables the recovery and refining of tin to obtain ingots of 99.90% purity or higher, as confirmed by X-ray fluorescence (XRF) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0059] In a specific embodiment, the method comprises:
a) granulating or shredding e-waste scrap to smaller particles (particulates) of e-waste;
b) subjecting the e-waste particulates obtained in step a) to magnetic separation, density-based separation, and separation in an eddy current separator;
c) optionally, subjecting the tin obtained in step b) to a thermal treatment at a temperature of about 300-400 °C;
d) subjecting the thermally treated tin obtained in step c) to vacuum distillation;
e) subjecting the tin obtained in step d) to chemical purification using a fluxing agent; and
f) subjecting the tin obtained in step e) to zone refining or linear crystallizing.

[0060] In a further specific embodiment, the method for recovering and refining tin from solder scrap comprises the following steps:
a) pre-treating solder scrap by subjecting e-waste to mechanical processing and optionally thermal treatment to remove impurities and undesirable materials and obtain tin-rich pre-treated metallic scrap; wherein the mechanical processing comprises granulating and separating tin-bearing materials from the solder scrap using one or more separation techniques selected from magnetic separation to eliminate ferrous contaminants, density-based separation to isolate heavier tin-lead alloy particles, and eddy current separation to separate non-conductive non-metallic parts;
b) subjecting the pre-treated metallic scrap obtained in step a) to a controlled refining process comprising vacuum distillation and chemical purification to obtain refined tin; wherein,
? the distillation comprises heating the tin-rich pre-treated metallic scrap at about 500-700 °C under a vacuum of about 0.01-0.1 mmHg to vaporize or oxidize volatile impurities comprising Zn, Pb, and/or Cd; and capturing the vaporized or oxidized impurities in one or more cold traps to prevent their release into the environment; and
? the chemical purification comprises adding a fluxing agent (mixture of ZnCl2 and NH4Cl) to the pre-treated metallic scrap in molten state simultaneously with or subsequent to the vacuum distillation; wherein the fluxing agent reacts with arsenic, copper, and/or iron to form a skimmed slag layer; and
c) subjecting the refined tin obtained in step b) to a post-processing step comprising zone-refining using a spiral zone refiner or a linear crystallizer having a rotating induction heating coil to obtain tin with enhanced purity; wherein the temperature is maintained from about 350 °C to about 450 °C along a spiral path.

[0061] In certain embodiments of the preceding embodiment, the zone refining is performed for two cycles in an inert atmosphere (N2); wherein the temperature at the hot end is maintained at about 400 °C, and the temperature at the cool end is maintained at about 200 °C; and induction coil traverses the tin mass at a rate of about 1-3 mm/min.

[0062] In certain embodiments of the preceding embodiment, tin has a purity of about 99.50% after step b) as confirmed by X-ray fluorescence (XRF) or inductively coupled plasma optical emission spectroscopy (ICP-OES). In some embodiments, the tin has a purity of about 99.90% purity or higher after step c), as confirmed by X-ray fluorescence (XRF) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0063] In certain embodiments, the method as described in any of the preceding embodiments, is carried out without the use of strong acids or cyanide-based reagents, and extremely high temperatures.

[0064] In another embodiment, the present disclosure provides tin obtained from the method as described in any one of the preceding embodiments.

[0065] The refined tin has a purity of at least 99.9% as confirmed by X-ray fluorescence (XRF) or inductively coupled plasma optical emission spectroscopy (ICP-OES). Trace impurities such as lead (Pb), antimony (Sb), iron (Fe), arsenic (As), zinc (Zn), and cadmium (Cd) are reduced to ppm (parts per million) or sub-ppm concentrations. Achieving such low impurity levels is critical, as even minor contamination can adversely affect the mechanical, electrical, and soldering properties of tin in sensitive electronic components.

[0066] The foregoing outlines features of several embodiments so that those skilled in the art better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other refining methods. Those skilled in the art should also realize that such equivalent modifications do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein.

[0067] The present disclosure is further described with reference to the following examples, which are only illustrative in nature and should not be construed to limit the scope of the present disclosure in any manner.

EXAMPLES
[0068] Example 1: Extraction of tin from solder scrap:
Stage 1:
Pre-Treatment
100 kg of solder scrap such as PCBs, solder joints etc. (approx. composition: 60% Sn, 38% Pb, 1% Cu/Fe, 1% others) is taken and crushed in a granulator. The scrap was crushed and size-reduced to a particle size of approximately 3 mm.

The granulated material was passed through a high-gradient magnetic separator to extract ferrous materials. A total of 0.5 kg of magnetic (ferrous) debris was recovered, corresponding primarily to embedded iron-containing fasteners and component leads. The non-magnetic fraction was subjected to density-based separation using a vibrating table to isolate heavier tin-lead alloy particles.

Following density separation, the intermediate product was processed through an eddy current separator to selectively eject non-conductive particles, including fine dust, plastic, ceramic fragments, PCB, and residual board material. The combined mass removed from the density-based and eddy current separations totaled 3.5 kg.

After the removal of magnetic, non-metallic, and low-density fractions, the remaining 96.0 kg of material comprised predominantly of tin-lead alloy particles.

Thermal Pre-Treatment:
The tin-rich metallic scrap was introduced into a rotary kiln and heated to a temperature of 350°C for 45 minutes under N2 atmosphere. As heating starts, contaminants like lead, cadmium, and arsenic volatilize or oxidize at lower pressures, separating from tin. This step captured and cooled volatilized impurities. A total of 1.2 kg of volatile organic matter was removed in this step. The resulting tin-rich metallic scrap was 94.8 kg.

Stage 2: Vacuum Refining + Chemical Purification
The pre-treated (tin-rich) metallic scrap was placed into a graphite crucible housed within a vacuum distillation unit or furnace. The vacuum distillation unit includes a heating chamber, condenser, and off-gas handling. The system was sealed and evacuated to a pressure of about 0.05 mmHg, and the material was heated to a temperature of 600°Cfor 2 hours to allow for the selective volatilization of lower-boiling-point metal contaminants, primarily lead (Pb), zinc (Zn), and cadmium (Cd). These elements vaporized under the reduced pressure and were transported via gas flow to cold trap condensers positioned downstream of the furnace chamber.

Approximately 8.2 kg of volatile condensate containing majorly Zn, Pb, and Cd was recovered from the cold traps, thereby significantly reducing the concentration of these contaminants in the tin matrix.

The remaining metal melt, now consisting primarily of tin with minor quantities of non-volatile impurities (e.g., Fe, As, Cu), was subjected to chemical purification. A fluxing agent blend consisting of 0.5 kg of ZnCl2–NH4Cl in a ratio of 1:1 was introduced into the molten tin under an inert nitrogen atmosphere to prevent re-oxidation. The fluxing agents selectively reacted with trace impurities to form stable slag complexes, which were lower in density and floated to the surface of the melt. After about 15 to 20 minutes, the slag layer was manually skimmed from the surface using non-reactive ladles. A total of 3.4 kg of slag was removed, enriched in iron, arsenic, and copper compounds. The purified metal (refined tin) was allowed to cool under inert gas and was cast into ingots. The yield of the refined tin was 83.2 kg, corresponding to an overall recovery efficiency of approximately 87.7% from the thermally treated input.

Chemical analysis of the final product confirmed a purity level of approximately 99.50 wt% tin, with residual lead content of <0.1 wt% and others < 0.4 wt% as confirmed by X-ray fluorescence (XRF) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

Stage 3: Zone Refining (Crystallization)
83.2 kg of refined tin containing residual trace impurities was subjected to a zone refining process. The equipment used comprised a spiral crystallizer fitted with a rotating induction heating coil. The crucible containing the refined tin was mounted on a turntable, which imparted a spiral motion to the molten zone, ensuring directional solidification from the central axis outward. The entire setup was housed in a sealed chamber and continuously purged with nitrogen (N2) to maintain an inert atmosphere, preventing oxidation during high-temperature operation.

A controlled thermal gradient was established, with the hot end maintained at approximately 400°C and the cool end at approximately 200°C, facilitating a gradual and directional solidification front. The induction heating coil was moved spirally at a rate of 2 mm/min, optimizing the redistribution of impurities and promoting cleaner crystallization of tin. The zone refining process was conducted over a total of 6 hours, with two complete zone passes performed across the length of the spiral ingot to maximize impurity migration and concentration at the tail end.

1.1 kg of impurity-enriched tail-end material was identified and mechanically removed. 82.1 kg of purified tin was obtained. Chemical analysis conducted using X-ray fluorescence (XRF) and inductively coupled plasma optical emission spectroscopy (ICP-OES) confirmed the purity of the product to be =99.90 wt% tin, with all residual contaminants (Pb, Fe, Cu, As, Zn) well below 0.1 wt%.
Yield: 82.1% from original input
Final form: Cast ingots of 10–15 kg each
Purity: >99.90% Sn
Appearance: Silver-white metallic ingots with smooth surfaces
Density: ~7.3 g/cm3
Conductivity: High (as per standard Sn metal values)
No toxic residues present
• Complies with RoHS and REACH benchmarks

Comparative Example:
The present method (Inventive Method) was compared with two commonly used methods in the tin recovery industry: 1. Pyrometallurgical Smelting; and 2. Hydrometallurgical Leaching. The experimental setup and results are provided in Tables 1 and 2, respectively.

Table 1: Experimental Setup
Parameter Inventive Method Pyrometallurgical Process Hydrometallurgical Process
Feedstock 100 kg e-waste solder scrap (60% Sn) Same Same
Pre- Treatment Mechanical + thermal (350°C, N2) None or basic crushing Acid leaching only
Core Refining Vacuum distillation @ 600°C + chemical
fluxing Smelting in open furnace @ 1100°C Leaching with HCl/HNO3, electrolysis
Post-
Purification Spiral zone refining (2
passes) Ingot casting Electro-winning
Chemicals ZnCl2/NH4Cl-based
flux (0.5%) Reducing agents,
limestone Strong acids (HCl,
HNO3), NaOH
Duration ~9 hours (total cycle) ~6 hours 20–24 hours
Waste
Treatment Inert slag, closed loop
gases Toxic fumes, slag Spent acids,
neutralization sludge

Table 2: Results
Attribute Inventive Method Pyrometallurgical
Process Hydrometallurgical
Process
Final Yield 82.1 kg 75–78 kg 65–70 kg
Purity of Tin 99.90% 95–97% 92–95%
Energy
Consumption Low (vacuum
@ 600°C) Very High (1100–
1200°C) Moderate
Chemical Waste Minimal,
recyclable Toxic slag, emissions High liquid waste
Environment
Impact Low High High
Cost per kg (est.) ?25–30/kg ?35–40/kg ?40–50/kg
Equipment Complexity Moderate (modular) High (furnace infrastructure) High (acid handling, electrolysis)

Conclusive Observations:
1. Purity & Quality Advantage:
The inventive method consistently achieves 99.90% Sn purity, which matches LME-grade specifications. Competing processes fail to deliver this level from e-waste sources without multiple cycles or external additives.
2. Yield Efficiency:
Inventive method gives the highest yield (82.1%), vs 75–78% in smelting and 65 to 70% in leaching due to incomplete recovery or acid losses.
3. Sustainability & Compliance:
Unlike conventional methods, the inventive process produces no toxic gaseous emissions or corrosive liquid effluents, making it REACH and RoHS compliant by design.
4. Economic Viability:
Lower energy input and modular equipment reduce operating costs by up to 30%, with faster break-even for commercial-scale units.

The integrated refining process of the present disclosure represents a marked technological improvement over known methods by achieving higher purity, better yield, lower energy use, and minimal environmental burden. , Claims:1. A method for refining tin from impure electronic waste (e-waste) scrap, comprising:
a) pre-treating e-waste scrap by subjecting e-waste to mechanical processing and optionally thermal treatment to remove impurities and undesirable materials and obtain tin-rich pre-treated metallic scrap;
b) subjecting the pre-treated metallic scrap obtained in step a) to a controlled refining process comprising vacuum distillation and chemical purification to obtain refined tin; and
c) subjecting the refined tin to a post-processing step comprising zone-refining using a spiral zone refiner or a linear crystallizer having a rotating induction heating coil to obtain tin with enhanced purity.

2. The method as claimed in claim 1, wherein in step a), the mechanical processing comprises granulating the e waste and separating tin-bearing materials from the e-waste scrap using one or more separation techniques selected from magnetic separation, density-based separation, eddy current separation, electrostatic separation, and gravity separation.

3. The method as claimed in any one of claims 1 to 2, wherein the thermal treatment is carried out at a temperature of about 300-400°C for about 30-60 min.

4. The method as claimed in any one of claims 1 to 3, wherein in step b), vacuum distillation comprises heating the tin-rich pre-treated metallic scrap at about 500-700 °C under a vacuum of about 0.01-0.1 mmHg.

5. The method as claimed in any one of claims 1 to 4, wherein in step b), chemical purification comprises adding a fluxing agent to the pre-treated metallic scrap in molten state simultaneously with or subsequent to the vacuum distillation; wherein the fluxing agent is capable of binding with metal impurities present in the molten material.

6. The method as claimed in claim 6, wherein the fluxing agent is capable of binding with arsenic, copper, and/or iron.

7. The method as claimed in claim 6, wherein the fluxing agent is a chloride salt selected from a group comprising ZnCl2, NH4Cl, NaCl, KCl, and combinations thereof.

8. The method as claimed in claim 1, wherein in step c), the tin material is caused to undergo spiral motion relative to the rotating induction heating coil.

9. The method as claimed in claim 8, wherein the spiral motion is generated mechanically or via a magnetically driven turntable.

10. The method as claimed in any one of claims 1 to 9, wherein in the zone refining step, the temperature is maintained from about 350 °C to about 450 °C along a spiral path.

11. The method as claimed in claim 1, wherein the zone refining is performed for two or more cycles.

12. The method as claimed in claim 1, wherein the zone refining is conducted in an inert atmosphere.

13. The method as claimed in claim 1, wherein the temperature at the hot end is maintained at about 400 °C, and the temperature at the cool end is maintained at about 200 °C.

14. The method as claimed in claim 1, wherein induction coil traverses the tin mass at a rate of about 0.5 mm/min to about 5 mm/min.

15. The method as claimed in claim 1, wherein it comprises:
a) granulating or shredding e waste to obtain particulate matter of e-waste;
b) subjecting the e-waste particulates obtained in step a) to magnetic separation, density-based separation, and separation in an eddy current separator;
c) optionally, subjecting the tin obtained in step b) to thermal treatment at a temperature of 300 to 400 °C;
d) subjecting the semi-purified tin obtained in step c) to vacuum distillation;
e) subjecting the tin obtained in step d) to chemical purification using fluxing agents; and
f) subjecting the tin obtained in step e) to zone refining or linear crystallizing.

16. The method as claimed in any one of claims 1 to 15, wherein the refined tin has a purity of at least 99.9% as confirmed by X-ray fluorescence (XRF) or inductively coupled plasma optical emission spectroscopy (ICP-OES).