Field of invention

This invention relates to collection of metal ions from solutions using a laser 3D printed porous body with a chemical functionality, the body made of at least one compound having selective properties for collecting chosen metal ion, to releasing the collected metal ions from the porous body as well as to a method for

manufacturing said porous body.

Background and prior art

Both pyrometallurgical and hydrometallurgical methods for recovering metals from various sources are currently used. (7) Often the collection of chosen metals or ions in liquid takes place presently in conventional columns filled with active powder or beads.

Patent US 9278338B2 presents 3D printing of catalyst, where ALM method is disclosed. The ALM method, which is also known as layer manufacturing, may be applied to catalyst design using known techniques. In order that the shaped unit has structural integrity, the powder material is bound or fused together as the layers are deposited. The process of layer deposition and binding or fusion is repeated until a robust shaped unit is generated. Several ALM binding and fusion fabrication techniques are available, notably 3D printing and laser sintering techniques. Any of the techniques may however be used.

Chinese document CN103751852A presents a preparation method of a three- dimensional artificial random porous structure tissue engineering scaffold, belonging to the technical field of biomaterials. The document aims to solve the design and manufacturing problems of the bionic structure of tissue engineering scaffold, provides a design method for constructing a random distributed scaffold porous structure with a bionic shape under expected porosity and pore size requirements, and molds by using a 3D additive manufacturing method to produce tissue substitute. The porosity of the structure is described by the aperture size being in a range of 1000 - 1500 μηι.

WO application WO2016188606A1 presents devices for substance separation prepared using 3D printed monolithic objects. The invention aims produce monolithic sorbents for chromatography or sample preparation. Chromatography is a technique where single components can be separated from a mixture. Column chromatography, where the monoliths described in the document are principally used, is based on stationary materials that retards components of a mixture to certain extent when the mixture is pushed through a column together with carrier solution (eluent). Importantly, the materials commonly utilized in chromatography and in the above application, will retard the substances for a certain time but are eventually eluted out of the material by the eluent. This limits the usability of this material to only chromatographic applications where the interactions between substrate and stationary phase are generally physical and reasonably weak.

Summary of the invention

The object of the invention is to present a porous body, method for manufacturing it and its use for collecting substance from source material. These objects are achieved by the features presented accompanying claims. Particularly the polymer particles in the porous body are connected to each other and they form themselves a uniform porous structure, and said active component has a property of ion exchange, which makes possible to strip chosen metal ions from the porous body.

One of the principal processes described in the invention is an approach in hydrometallurgical treatment of metal containing materials, such as electronic waste, to prepare efficient, selective, and simple collector for capturing the metals, such as gold, platinum and palladium from complex mixture of dissolved metal ions. The method may naturally be applied for recovering other metals, such as Fe, Co, Ni, Cu, Ru, Rh, Ag, Re, Os, Ir, Hg, Sc, La-Lu, U and Th.

The invention discloses laser 3D printed, preferably manufactured using selective laser sintering (SLS) technique, chemically functional porous objects, which act as collectors for recovery of metal ions. Importantly, the collection of the metal ions is achieved by chemical interaction (bond formation, electrostatic interaction and/or weak interactions by van der Waals or dispersion forces) with the functional component of the porous object. Hence, the metal ions are tightly bound to the porous material and can be stripped off only by using separate, tailored solution.

Particularly, a method for manufacturing chemically functional SLS 3D printed porous body and utilizing it for selective recovery of gold, platinum and palladium ions from solution and the release of the metal ions from the said porous body, has been developed.

The porous body

A porous body with chemical functionality is provided according to claim 1. The polymer particles are connected to each other and form themselves a uniform porous structure. In a preferred embodiment said particles are mainly untouched and connected to each other on only a small fraction of the total surface and forming a coarsily lattice like structure. In addition to a designed mesh structure, a proper control of SLS-device may create an uniform, porous structure with high body having a porosity, defined as volume of voids over total volume, between 10 and 70 %. The powder is heated only in such extent, where particles are smelted slightly in order to connect them to each other. The contact surface to each next particle in only a small fraction of the total surface of a particle (typically 1 - 10 %).

According to advantageous but non-essential features of the invention, the porous body incorporates one or more of the following characteristics:

• Said body has thickening forms solid walls encompassing the porous portion.

The liquid may be poured or pumped through the object.

• Said polymer has the particle size in a range of 10 - 200 μηι, preferably in a range of 15 - 100 μηι and most preferably in a range of 20-80 μηι.

• The particles have optimum shape of a spherical body, but in practice there are deviations of dimensions in a range of 5 - 200 %, preferably 60 - 140 % of the average diameter of particles.

• Said body is composed of a polymer and/or chemically active component belonging to the group of polyamides (Nylon®), when gold is recovered.

• Preferably said polymer or chemically active component is Nylon 12 [poly(dodecano-12-lactam)], when gold is recovered.

• Said body contains 1-100 %, preferably 2-50 % and more preferably 5-30 % of chemically active component that belongs to group of ion exchange materials when platinum and palladium is recovered.

• Said chemically active component belongs to the group of type-1 anion exchanger resins (Dowex® 2 IK) when platinum and palladium is recovered. • Said body contains 1-100 %, preferably 2-50 % and more preferably 5-30 % of chemically active component that belongs to group of phosphoric or phosphonic acids when uranium is recovered.

• Said chemically active component belongs to the group of bis(phosphonomethyl)alkylamines when uranium is recovered.

• Said body contains 1-100 %, preferably 2-50 % and more preferably 5-30 % of chemically active component that belongs to a group of transition metals.

• Said chemically component belongs to a group noble metals (Cu, Ru, Rh, Pd, Ag, Re, Os, Pt, Au, Hg).

• Said chemically active component forms strong enough interactions with the metal ions that collected metal ions are not released from said body by the solution of which the metal ions are collected.

• Said body has a maximum dimension limited only by printer capacity.

Currently typical printable bodies range of 5 - 500 mm in the transverse direction of through flow and in a range of 5 - 500 mm in the direction of through flow.

• Said body may have interlocking members or connections for tubing to form an assembly of bodies or connect the body to pumping system.

• Said body may have designed interior channels or mesh to improve the flow and reduce the back pressure.

In another embodiment a porous body has an essentially defined structure achieved by the laser printing of sequential layers, each having a defined layout. Thus, porosity of inner and outer layers can be adjusted accurately.

In another embodiment are integral walls encompassing a porous center portion. The walls have a non-porous structure and thus they form a channel for a liquid. In another embodiment the active component belongs to a group of phosphoric or phosphonic acids, preferably to a group of bis(phosphonomethyl)alkylamines.

The properties of the porous body are efficiently controllable in a macroscopic using computer-aided design (CAD) and in a microscopic scale by fine tuning the parameters of the 3D printer.

The macroscopic control includes the design of shape, inner and outer structure of the body, size and functional parts, such as connections only limited by the available 3D printer.

The microscopic control includes design of the porosity and chemical properties of the body limited only by the intrinsic physical and chemical properties of the raw materials such as particle size and shape, melting/glass transition temperature and chemical functionality.

The porous body can be reused under continuous flow conditions. The flow properties of the object can be adjusted by designing interior flow channels and/or by adjusting the printing parameters.

Inactivated inner surface of the porous can be reactivated simply by removing the inactivated layer revealing fresh active surface. Removal of the inactivated surface can be carried out by using mineral acid or acid mixtures, typically nitric acid at concentrations of 0.5-8 M. Also organic solvents such as alcohols, typically methanol or ethanol, can be used for removal of the inactivated layer.

If the body is mechanically damaged beyond use, it can be grinded into powder with particle size of 20-80 μηι and used again as printing material.

Method for manufacturing the porous body

Method for manufacturing a chemically functional porous body for selective collection of metal ions from a liquid is described, where the selective body is manufactured by SLS 3D printing using at least one compound giving said selective properties and at least one substance forming structure for the body in 3D printing.

The polymer powder has the particle size preferably in a range of 10 - 200 μηι, more preferably in the range of 20 - 80 μηι. With smaller particle size, smaller channels and larger reactive surface area is achieved.

According to one embodiment of the invention the polymer is a part of a mixture having other substances. A salt may be used, where it can be dissolved, and the porous structure remains.

In another embodiment the walls encompassing a porous center portion are manufactured integrally in the porous body. This is achieved preferably so, that said SLS 3D printing parameters are adjusted to melt polymer powder fully in the area of walls (18) representing 100 % power of laser and to use 15 - 80 %, preferably 30 - 70 % power for porous center portion (13). The temperature of the chamber was 2 - 25 °C, preferably 5-20 °C below the melting point.

It was found that to obtain impermeable, solid material, the printing temperature was selected to be 2-25 °C, preferably 5-20 °C below the melting temperature (or in certain cases glass transition temperature) of the printable polymer and 100 % laser power and laser speed between 400-1200 mm s ^"1 was used. In contrast, to obtain porous material the laser power was lowered to 30-70 % and the rate was increased to 1600-2560 mm s ^"1 while the temperature remained in the same range. The most of particles (usually 70 - 100%, preferably 90 - 100%) are partly sintered so that they are connected to each other by only a small fraction of the total surface and they form a lattice like structure. The mechanical strength of the porous body, particularly inside integral walls has not been an issue even in the lightest, i.e. the most porous body. This forms an efficient method to achieve coarsely a lattice like structure for industrial use. The thickness of the wall in commercial solutions is preferably 0.1 - 7 % and more preferably 0.3 - 4 %, of the diameter of the porous portion.

The density of a porous body can be defined as percentage compared to the impermeable, solid material (fully melted) as inverse of the porosity which in turn is defined as volume of voids over total volume of the object. Hence, the density of the porous body is commonly 30-90 % of the density of fully melted material, such as impermeable walls as described above.

The absolute density values are dependent on the materials used, namely sinterable polymer and chemically active component. The density of a body with porosity of 30 %, mainly composed of standard polymer, such as polyamide or polypropylene, is preferably between 0.3 - 0.8 g/cm ³ and more preferably 0.4 - 0.6 g/cm ³ . The density of the fully melted material of standard polymers is 1.01 g/cm ³ and 0.946 g/cm ³ for polyamide and polypropylene, respectively. The test bodies were measured and following density values of porous body were found: polyamide (PA): 0.45-0.6 g/cm ³ and polypropylene (PP): 0.35-0.65 g/cm ³

Method for collecting metal ions from solution using laser 3D printed porous body

The active material is printed in various forms and porosities hence the metal ion containing solution can be passed through it by gravitational force or by pumping or the material can be submerged to solution containing the target substance.

The overall metal collecting process comprises steps of:

• crushing and sieving the source material to obtain sieved source mass • leaching the sieved source mass to obtain a liquid containing the chosen metals or ions,

• providing a porous body according to this invention

• separating chosen metal ions due to adsorption, size and/or chemical interaction with the porous body

• stripping chosen metal ions from the porous body (10).

The first two steps are not needed when separation is carried for example from liquid source material, such as mining raffinate, industrial process water or wastewater.

When the recovery of gold is the target, the polymer powder and/or chemically active component contains preferably at least one polymer belonging to a group of poly amides (Nylon®). From the group of poly amides most preferable is Nylon 12 [poly (dodecano- 12-lactam)] .

When the recovery of palladium or platinum is the target, the chemically active component preferably belongs to group of ion exchange materials. Preferably said chemically active component is type-1 anion exchanger resin (Dowex® 2 IK).

When the recovery of uranium is the target, the chemically active component preferably belongs to the group of phosphoric or phosphonic acids. Preferably said chemically active component is bis(phosphonomethyl)dodecylamine.

After collection, the metal ions can be recovered by suitable stripping solution that is different compared to the solution of which the metals were collected.

When stripping of gold is targeted, the solution is preferably 1-15 M nitric acid, more preferably 3-10 M nitric acid and most preferably, 6-8 M nitric acid. When stripping of palladium is targeted, the solution is preferable 0.01-4 M thiourea water solution, more preferably 0.05-2 M thiourea water solution and most preferably 0.1-0.5 M thiourea water solution.

When stripping of platinum is targeted, the solution is preferable 0.01-4 M thiourea water solution, more preferably 0.05-2 M thiourea water solution and most preferably 0.2-0.8 M thiourea water solution.

The porous body is reusable for metal ion collection after the collected metals or ions have been removed.

If the chemically active component is ion exchanger, regeneration using mineral acid is needed. Hydrochloric acid is used with concentration of 0.01-8 M, more preferably 0.05-4 M and most preferably 0.1-0.5 M.

Chemically functional laser 3D printed objects can also be used in cases where initial substances fed to the printed object are converted to another chemical compounds or ions and eluted through the body or collected by the body.

Chemically active component can be mixed with the printing material that can be polymer, ceramics or metal, to get chemically, photochemically or biologically active hybrid material containing metals or metal compounds such as Ni, Zr or platinum group metals typically Pt, Pd or Rh. The typical concentration of the added metal or metal compound range from 0.5-10%. The chemical reaction is performed in the object in a continuous flow process resulting in products converted from the original compounds to other substances. The effectivity of the laser 3D printed object is based on high and adjustable surface area and porosity of the object.

Brief Description of the Several Views of the Drawing The Invention is further illustrated by reference to the Figures in which;

Figures la and lb present SLS 3D printed flow through object

Figure lc presents the 3D printed mesh with integrated walls

Figures 2a and 2b present helium ion microscope (HIM) images of the break surface of 3D printed collector

Figure 3a presents X-ray tomographic image of a cylinder shaped SLS 3D printed porous metal ion collector and anion exchange resin

Figure 3b presents air structure diameter (pore size) distribution of the object

SLS 3D printed porous body.

Figures 4a - 4c present HIM images taken from objects printed with SLS technique using Nylon 12 powder (50 μηι particle size), and wherein.

Figure 5 depicts recovery profiles from the test solution (green) and leached electronic waste (blue) after treating the samples with Nylon- 12 powder.

Figure 6a depicts recovery profiles from the test solution after treatment with porous SLS 3D printed object containing palladium and platinum selective component

Figure 6b presents the compositions of stripping solutions.

Figure 7 presents a process for recovering Au, Pt and Pd from a mimic of an electronic waste leachate.

Detailed Description of the Invention Example 1

A porous body with chemical functionality is manufactured using selective laser sintering (SLS) 3D printing with Sharebot SnowWhite 3D printer. A mixture of polypropylene (AdSint PP flex by ADVANC3D Materials®) and grinded type-1 anion exchange resin (DOWEX 2 IK®) is prepared by thorough mechanical stirring. This material is placed to Sharebot SnowWhite 3D printer and printed to desired shape using 0.1 mm layer thickness, laser power of 40 % of the maximum power with the laser rate of 2400 mm s ^"1 . Build plate temperature of 119-123 °C was used. For computer aided design (CAD) and slicing, FreeCad v. 0.16 and Slic3r v 1.2.9 were used, respectively.

Figure la presents SLS 3D printed flow through object (10) for collecting gold from solution with 3D printed hose connectors (11), and figure lb presents a split body showing the interior structure with impermeable walls (12), highly porous interior for collection metal ions (13) and flow channels for the solution (14). The whole object is printed as a single object using Nylon 12.

Instead of arbitrary mesh structure a well-organized mesh can be manufactured by 3D printing as in figure lc. It has thickening in an outer circle forming walls 142 encompassing a channel of a porous portion 141. The funnel 16 at the bottom restricts the flow, and the mesh 14 (here length 35 mm, diameter 27 mm) works as the functional part of the collector. The reservoir 12 at the top is used to load the sample into the column.

Figure 2a presents a helium ion microscope (HIM) images of the break surface of 3D printed collector with overall porous structure and figure 2b presents tightly attached collector material (DOWEX® 21K CI anion exchange resin) is shown as light-colored particles 21. Figure 3a presents X-ray tomographic image of a cylinder shaped SLS 3D printed porous metal ion collector prepare of non-functional polypropylene (31, dark shapes) and figure 3b presents air structure diameter (pore size) distribution of the object SLS 3D printed porous body.

Figure 4a presents a zoom in view on a porous object showing that the printing material has retained its particle-like structure in printing with low laser and high rate in normal temperature (30 %, 2560 mm/s and 166 °C, respectively). Separate particles 21 are clearly visible and their minimal contact to each other.

Figure 4b presents a break surface of a porous object (taken from the inside of a cylinder- shaped object) printed with low laser and high rate in normal temperature (30 %, 2560 mm/s and 166 °C, respectively).

Figure 4c presents an image of a low-porosity wall of an object printed with high laser power and slow rate in normal temperature (100 %, 1200 mm/s and 166 °C, respectively) using SLS 3D printer (for example Sharebot Snow White).

As from figure 5 the claimed method gives excellent recovery selectivity of gold. Figures 6a and 6b reveal good performance also in recovery of palladium and platinum.

Figure 7 presents a process for recovering Au, Pt and Pd from a mimic of an electronic waste leachate. PA: Porous SLS 3D printed porous gold selective Nylon 12 object. 1-PP: Porous SLS 3D printed objects manufactured using mixture of polypropylene and type-1 anion exchange resin for recovering Pt, Pd and Sn. Pt, Pd and Sn are released from the object one-by-one by using different stripping solutions.

Example 2 A porous body with chemical functionality and solid walls is manufactured from Nylon 12 (AdSint PA 12 by ADVANC3D Materials®) by placing the polymer to Sharebot Snow White 3D printer and printing it to desired shape using 0.1 mm layer thickness. The outer layers (3-15, the number depends on the complexity of the design) are defined during the slicing of the CAD model. For these layers, forming the impermeable walls, laser power of 100 % of the maximum power with the laser rate of 800-1200 mm s ^"1 is used. For porous interior structure (all areas that were not defined as outer layers during the slicing of the CAD model), capable of collecting gold, laser power of 30-40 % of the maximum power with the laser rate of 2400-2560 mm s ^"1 is used. Build plate temperature of 158-163 °C was used. For CAD and slicing, FreeCad v. 0.16 and Slic3r v 1.2.9 were used, respectively.

Example 3

A porous body composed of solely on one polymer (Nylon 12) was used for gold recovery. The experiment was conducted using SLS 3D printed object and a test solution imitating dissolved waste electric and electronic equipment (WEEE). The test solution contained 100 ppm of Ni, Zn, Fe, Cu and 50 ppm of Al, Cr, Pb and Sn along with 5 ppm of Pd, Pt and Au in 5 % acid media (mixture of hydrochloric and nitric acid). 20 ml of solution was placed in a 50 ml centrifuge tube containing mesh shaped porous body. Tube was sealed and agitated using Stuart SF1 at 500 osc min-1 for 24 hours. ICP-OES analysis revealed that virtually all (99 %) gold was removed from the solution while all other metal ions remained in the solution.

Similar extraction study was performed using authentic WEEE solution prepared using ultrasound-assisted acid leaching. From this material, about 80 % of gold was collected without notable contamination by any other metals such as copper (concentration over 300 times larger than Au).

Example 4 A porous body composed of polypropylene as sinterable polymer and type 1 ion- exchange resin (DOWEX 2 IK®) as chemical functionality, was used for palladium and platinum recovery. The experiments were conducted by placing SLS 3D printed filters in a syringe. WEEE test solution (as described above) was pushed through and the metal concentrations were measured before and after the adsorption experiment. Over 96 % of Pd and 98% of Pt were removed from a solution containing 20 to 200 times higher concentrations of other metals such as aluminium, iron and copper.

Example 5

A porous body composed of polypropylene as printable polymer and bis(phosphonomethyl)dodecylamine as molecular chemical functionality, was used for uranyl recovery. The experiments were conducted by placing SLS 3D printed filters in a syringe. A solution imitating a mining leachate was then pushed through and the metal concentrations were measured before and after the adsorption experiment. About 85 % of U, 95 % of Sc and 70 % of Fe were removed from a solution containing various other metals such as aluminium, cobalt, copper and rare earth elements.

Example 6

Stripping of selected metals (Pd, Pt) from a porous body, composed of polypropylene as sinterable polymer and type 1 ion-exchange resin (DOWEX 2 IK®) as chemical functionality, was initiated by six washing cycles with water, followed by four cycles of 0.1 M thiourea to strip almost 90 % of trapped palladium. Next, four cycles of 0.3 M thiourea stripped most of the platinum in the object (about 50 % of total recovered amount). Finally, four cycles of 4.5M HN03 removed all tin with small amounts of other trapped metals. The filters were regenerated by passing 0.1 M HC1 through the object. References and Notes:

1. M. Kaya, Recovery of metals and nonmetals from electronic waste by physical and chemical recycling processes. Waste Manag. 57, 64-90 (2016).

Modified embodiment (this is not a part of this invention)

Chromatographic elements (as shown US 2018/0126298 Al) could be made more efficiently by a modified method. The thermoplastic polymer is selected from the group of the polyether imides, polyarylates, polyether ketones, polyesters, polyamides, polyimides, polyamide imides, polybenzimidazoles, polyphenylene sulfides, polyphenyl sulfones or polyoxymethylene as well as mixtures of two or more of these materials.

While the porous bodies according to invention are wide compared to height in typical industrial use, chromatographic elements are very high compared to their transverse dimension (say the height is 20 - 200 times their diameter.

An ion exchanger is not used and such material is not needed.

Again, coarsely a lattice like structure made by 3D printing with limited laser power, whereby particles remain nearly untouched, when connected to each other. Each particle connects to each other only on a small portion of its surface.

Preferable particles size is bigger than in the invention being 100 - 400 μηι.