Bayer process
The standard industrial method for purifying bauxite ore into alumina powder, using hot caustic soda to dissolve the aluminium and leave the impurities behind.
Technisch gezien: The Bayer process is the dominant commercial route for producing metallurgical-grade alumina from bauxite, comprising four principal stages: digestion of crushed bauxite in hot concentrated sodium hydroxide solution to dissolve aluminium-bearing minerals as sodium aluminate; clarification and washing to separate the insoluble residue (red mud or bauxite residue); precipitation of aluminium hydroxide from the cooled, seeded liquor; and calcination of the hydroxide to anhydrous alumina. The process is selective for gibbsite, boehmite and diaspore but is less effective on silica-rich bauxites because silica reacts with caustic to form desilication products that consume reagent and reduce yield.
Processing
HPAL
A process that uses a pressurised vessel filled with very hot, oxygen-rich acid to dissolve nickel and cobalt out of a type of ore that is otherwise hard to treat.
Technisch gezien: High-pressure acid leach is an autoclave-based hydrometallurgical process in which laterite ore is leached with sulfuric acid at elevated temperature and oxygen partial pressure, conditions that dissolve nickel and cobalt selectively relative to iron. The high operating temperature is necessary because nickel-bearing minerals in limonite and saprolite laterites are insufficiently reactive under atmospheric leach conditions. HPAL is distinguished from atmospheric heap or vat leaching not merely by pressure but by the consequent change in iron chemistry: at HPAL conditions, dissolved iron precipitates as hematite within the autoclave rather than contaminating the pregnant liquor.
Processing
Hall-Héroult process
The only widely used method for making aluminium metal, passing electricity through dissolved alumina to split it into molten aluminium and carbon dioxide gas.
Technisch gezien: The Hall-Héroult process is the electrolytic reduction of alumina dissolved in molten cryolite (sodium aluminium fluoride) at around 960 °C, in which direct current causes aluminium ions to deposit as liquid metal at the carbon cathode while oxygen is discharged at the carbon anode, reacting with the anode to produce carbon dioxide. It is an energy-intensive operation; electricity is the dominant operating cost and the largest contributor to the carbon footprint of primary aluminium production. The process is occasionally confused with electrorefining, but Hall-Héroult produces primary metal from an oxide feedstock rather than purifying a crude metal anode.
Processing
Kroll process
The standard way of making titanium metal, replacing titanium's bond to chlorine with a bond to magnesium and then separating the result to leave spongy titanium metal.
Technisch gezien: The Kroll process is a batch pyrometallurgical reduction in which titanium tetrachloride vapour is reacted with liquid magnesium metal in a sealed, inert-atmosphere retort to yield titanium metal and magnesium chloride; the magnesium chloride is then drained and the residual magnesium recovered by vacuum distillation, leaving a porous titanium mass known as sponge. The process remains the predominant industrial route for primary titanium despite its batch nature and high energy demand, because titanium's extreme reactivity toward oxygen and nitrogen at elevated temperature makes continuous melting or aqueous routes difficult to implement at commercial scale. The magnesium chloride by-product is typically electrolysed to regenerate both magnesium and chlorine for recycle.
Processing
SX-EW
A way of pulling copper out of a liquid using special chemicals, then using electricity to turn it into pure sheets of metal — no smelting needed.
Technisch gezien: Solvent extraction–electrowinning is a two-stage hydrometallurgical route in which a pregnant leach solution is contacted with an organic extractant to selectively concentrate the target metal into a loaded organic phase (solvent extraction), which is then stripped and fed to an electrowinning cell where the metal deposits onto a cathode. In copper production it is most commonly paired with heap or dump leaching of oxide or secondary sulfide ores. It is sometimes conflated with electrorefining, but electrorefining purifies an already-cast anode whereas electrowinning deposits metal directly from solution.
Processing
Siemens process
A method of making very pure silicon by decomposing a silicon-containing gas onto hot rods and gradually building up thick rods of high-purity silicon.
Technisch gezien: The Siemens process produces polycrystalline silicon of semiconductor or solar-cell grade by the chemical vapour deposition of trichlorosilane — or, in some variants, silane — onto electrically heated silicon slim rods in a sealed reactor, with hydrogen as the carrier and reducing gas; silicon deposits progressively on the rod surface until rods of the required diameter are harvested. It is distinguished from metallurgical-grade silicon production, which uses carbothermic reduction in an electric arc furnace and yields a far less pure product. The process is energy-intensive and generates tetrachlorosilane as a significant by-product, the handling and recycling of which has a material effect on overall process economics and environmental performance.
Processing
anode
The impure block of metal that slowly dissolves away during electrorefining. Electricity pulls metal atoms off it and deposits them, in purified form, onto the cathode on the other side of the tank.
Technisch gezien: In electrorefining, the anode is the positively charged electrode, cast from blister or fire-refined copper, that undergoes oxidative dissolution as the current drives metal ions into solution. Its composition determines which impurities accumulate in the electrolyte and which collect as anode slime beneath or around it. The term is also used in electrowinning, but there the anode is an inert or dimensionally stable electrode that does not dissolve; confusing the two contexts matters because anode behaviour and anode slime generation are specific to electrorefining only.
Processing
anode slime
A muddy residue that collects under the dissolving anode during electrorefining. It contains impurities and sometimes valuable materials such as silver and gold that did not dissolve into the liquid.
Technisch gezien: Anode slime is the solid residue that accumulates at the base of the anode or on the cell floor during copper electrorefining, composed of anode constituents that are insoluble under the operating conditions of the electrolyte—typically selenium, tellurium, lead sulfate, and the precious metals silver, gold, and platinum-group elements. Recovery of these by-products from anode slime is often an economically significant part of a copper refinery's operation. The composition and quantity of anode slime are direct functions of the anode chemistry, making anode quality control important for by-product recovery planning.
Processing
autoclave
A sealed, pressurised vessel that lets water be kept much hotter than its normal boiling point, so that reactions happen faster or at all.
Technisch gezien: In metallurgical processing an autoclave is a pressure vessel in which aqueous leaching is conducted at elevated temperature and partial pressure of oxygen or steam, allowing solution temperatures well above the atmospheric boiling point of water and enabling oxidation or dissolution reactions that are thermodynamically or kinetically impractical at ambient pressure. The term describes the vessel itself, though it is commonly used as shorthand for the pressure-leach operation performed within it. It should not be conflated with a simple heated leach tank; the defining characteristic is that the system operates above ambient pressure, which fundamentally alters both the chemistry and the engineering requirements.
Processing
blister copper
Copper that is nearly pure but still has small amounts of impurities trapped inside it. Its bumpy, blistered surface—caused by gas bubbles escaping as it solidifies—gives it its name.
Technisch gezien: Blister copper is the product of converting copper matte in a Pierce-Smith or similar converter, in which iron sulfide is progressively oxidised and slagged off, leaving a crude copper metal typically containing small but commercially significant quantities of sulfur, oxygen, and trace impurity metals such as gold, silver, arsenic, and bismuth. The characteristic blistered surface forms because dissolved sulfur dioxide escapes during solidification. Although high in copper content, blister copper requires fire refining and then electrorefining before it meets the purity specifications of cathode copper traded on commodity markets.
Processing
calcination
Heating a mineral strongly enough to drive off gases — often water vapour or carbon dioxide — without actually melting it.
Technisch gezien: Calcination is a thermal treatment carried out below the fusion point of the material, with the primary purpose of driving off volatile components such as chemically bound water, carbon dioxide or sulfur dioxide, thereby transforming the feed into a more reactive or chemically altered solid product. It is routinely confused with roasting: the distinction is that calcination targets decomposition or dehydration rather than oxidation of a sulfide or other reactive species. In the Bayer process, for example, aluminium hydroxide is calcined to produce anhydrous alumina.
Processing
cathode
The clean sheet of metal that pure metal grows onto during electrorefining or electrowinning. At the end of the process the cathode is the finished, high-purity product.
Technisch gezien: In electrometallurgy, the cathode is the negatively charged electrode onto which metal ions from the electrolyte are reduced and deposited as solid metal. In copper production the term 'cathode' is used both for the electrode itself during the process and for the flat, high-purity copper product that is sold after it is stripped from the starting sheet. Cathode copper is the standard tradeable form of refined copper and must meet published purity specifications to qualify for exchange-registered delivery; it is sometimes confused with the anode, which is the dissolving or oxidising electrode carrying the opposite charge.
Processing
cathode active material
The powder inside a battery's positive end that actually stores and releases electrical energy by holding onto lithium ions when the battery is charged.
Technisch gezien: Cathode active material (CAM) is the lithium-bearing oxide or phosphate compound that forms the electrochemically active component of the positive electrode in a lithium-ion cell, accepting and releasing lithium ions during discharge and charge respectively. Common CAM chemistries include lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminium oxide (NCA), and lithium iron phosphate (LFP), each with different trade-offs in energy density, thermal stability, and cycle life. CAM is distinct from the precursor cathode active material (PCAM) from which it is synthesised and from the finished electrode, which also contains binder, conductive carbon, and a current collector.
Processing
concentrate
The valuable mineral-rich material collected after processing ore. Think of it as the useful part that has been separated from most of the waste rock, ready for the next stage of treatment.
Technisch gezien: A concentrate is the product of a beneficiation step—commonly flotation or gravity separation—in which the grade of the target mineral or metal has been substantially raised relative to the run-of-mine ore, and most gangue has been discarded as tailings. Concentrates are defined by their contained metal grade and penalty element levels, which govern their commercial value and smelter treatment charges. The term is distinct from 'ore': ore refers to mineralised rock in the ground or as mined, while concentrate is an intermediate, processed product.
Processing
conversion
A processing step that changes a material from one chemical form into another so it is ready for the next stage — like turning a metal ore into a gas that can be sorted by weight.
Technisch gezien: In the nuclear fuel cycle, conversion refers specifically to the chemical process by which uranium oxide concentrate (yellowcake) is purified and reacted to form uranium hexafluoride (UF₆), the gaseous compound required as feed for enrichment. Outside the nuclear industry the term is used more broadly for any stage that transforms a material into a chemically distinct intermediate suited to downstream processing, such as the conversion of ilmenite to synthetic rutile or titanium tetrachloride. The nuclear-fuel sense is the most precisely delimited and is the one most often intended when the word appears alongside 'enrichment' and 'yellowcake' without further qualification.
Processing
doré
A rough bar of mixed gold and silver, still containing impurities, poured at a mine before being sent to a refinery to be separated and purified into pure metals.
Technisch gezien: Doré is an unrefined alloy of gold and silver, typically cast as bars at the mine or smelter following the processing of ore through leaching, gravity concentration, or pyrometallurgical routes. Its composition varies widely depending on the ore source, and it commonly contains minor quantities of base metals, sulfur compounds, and other impurities. Doré is the standard form in which gold and silver leave most mine sites for delivery to an independent bullion refinery, where the two precious metals are separated and brought to commercial purity; it is therefore a mine product and a refinery feed rather than a finished metal, and its value is assessed on the basis of assayed precious-metal content less refining charges.
Processing
electrorefining
A way of purifying metal using electricity. An impure block of metal slowly dissolves in a liquid, and the pure metal re-forms on a clean sheet nearby, leaving the impurities behind.
Technisch gezien: Electrorefining passes a direct current through an electrolyte solution between an impure metal anode and a pure metal starting cathode, causing the anode to dissolve and the target metal to deposit selectively onto the cathode at a purity that can exceed the anode grade. Base metals more noble than copper remain undissolved, while less noble metals dissolve but do not deposit under the controlled voltage conditions, accumulating instead in solution or in the anode slime. The process is distinct from electrowinning, in which metal is deposited from a leach solution rather than from a dissolving metal anode.
Processing
enrichment
A process that increases the proportion of one particular variety of an element relative to the others — in uranium, that means increasing the share of the type of atom that can sustain a nuclear reaction.
Technisch gezien: Enrichment, in the context of nuclear materials, is the process of increasing the concentration of fissile uranium-235 relative to the more abundant uranium-238, most commonly by gaseous diffusion or gas centrifuge acting on uranium hexafluoride. Natural uranium contains a low proportion of U-235; most reactor designs require a higher proportion, and weapons-grade material requires a much higher proportion still. The term should not be confused with beneficiation or upgrading of metallic ores, where 'enrichment' is sometimes used loosely to mean increasing the grade of a concentrate; in nuclear fuel-cycle reporting, enrichment has a precise quantitative meaning expressed as assay in weight percent U-235.
Processing
ferroalloy
An iron-based mixture that contains large amounts of another element — like manganese or chromium — and is added to steel during steelmaking to give the steel special properties.
Technisch gezien: A ferroalloy is a binary or more complex alloy of iron with one or more alloying elements — including manganese, silicon, chromium, nickel, molybdenum, vanadium, niobium, or others — produced in submerged-arc or electric-arc furnaces by smelting ore or oxide feeds in the presence of a reductant, typically coke. Ferroalloys are used almost exclusively as addition agents in steelmaking and cast-iron production, delivering the alloying element in a form that is easier to handle, store, and introduce to a melt than the pure metal alone. The distinction from master alloys is one of base metal and industry: ferroalloys are iron-based and directed at steel production, while master alloys are typically based on aluminium, copper, or nickel and used in non-ferrous foundry and casting operations.
Processing
flotation
A way of separating useful minerals from waste rock by mixing crushed ore with water and chemicals, then blowing in air bubbles. The mineral particles stick to the bubbles and float to the surface, while the waste sinks.
Technisch gezien: Froth flotation exploits differences in the surface chemistry of mineral particles: reagents called collectors make target mineral surfaces water-repellent, so air bubbles attach to them and carry them into a froth layer that overflows the cell, while hydrophilic gangue particles settle. The process is selective rather than universal—reagent choice and pH must be matched to the specific mineralogy—and the recovered froth product is called a concentrate. Flotation is sometimes confused with gravity separation, which instead exploits density differences and uses no reagents.
Processing
hydrometallurgy
Extracting metals by dissolving the ore in liquid and then recovering the metal from that liquid, rather than by melting anything.
Technisch gezien: Hydrometallurgy encompasses the aqueous processing routes used to extract, separate and recover metals, typically operating at or near ambient temperature and pressure — though pressure leaching is a significant exception. The three principal unit operations are leaching (dissolution of the metal into solution), solution purification and concentration (e.g. solvent extraction, ion exchange), and metal recovery (e.g. electrowinning, precipitation, cementation). It is distinguished from pyrometallurgy by the working medium — water-based solutions rather than high-temperature melts or gases — and the two are frequently combined in sequence within a single flowsheet.
Processing
leaching
Dissolving the useful metal out of ore or crushed rock using a liquid, usually an acid or an alkaline solution. The metal passes into the liquid and can then be collected from it.
Technisch gezien: Leaching is a hydrometallurgical operation in which a lixiviant—most commonly sulfuric acid for copper oxide ores, cyanide solution for gold, or caustic soda for bauxite—is brought into contact with crushed or run-of-mine ore to dissolve the target metal selectively into solution. The resulting pregnant leach solution is then processed by solvent extraction, ion exchange, or direct electrowinning to recover the metal. Leaching is the first step in a hydrometallurgical route and is used where ore mineralogy or grade makes pyrometallurgical processing uneconomic; it is operationally distinct from smelting, which requires heat rather than chemical solvation.
Processing
master alloy
A ready-made mixture of metals with a higher concentration of an additive than you want in the final product, so that a metalworker can stir in a small, precise amount and get exactly the right composition.
Technisch gezien: A master alloy is a pre-alloyed intermediate, usually based on aluminium, copper, or nickel, that contains a high concentration of one or more alloying or grain-refining elements and is formulated to dissolve readily when added in controlled quantities to a larger melt. The dilution approach allows precise compositional adjustment without the difficulty of handling small quantities of reactive or refractory pure metals directly. Master alloys are distinguished from ferroalloys by their non-ferrous base and by the relatively small addition rates typically involved; they are also distinct from hardeners in some industry usages, though the terms overlap in non-ferrous foundry practice.
Processing
matte
A thick, heavy liquid produced partway through smelting sulfide ores, made mostly of metal sulfides mixed together. It still needs further treatment before pure metal can be extracted from it.
Technisch gezien: Matte is an intermediate pyrometallurgical product consisting predominantly of metal sulfides—in copper production, mainly copper sulfide and iron sulfide—formed when a sulfide concentrate is smelted under controlled oxidising conditions. Its grade is expressed as the percentage of copper (or nickel, in nickel smelting) it contains, and raising this grade is the objective of the converting step that follows. Matte is distinct from slag, which is the silicate-dominated waste layer that separates above or below it in the furnace depending on density relationships.
Processing
precursor
A material that has been prepared partway through a process and is ready to be turned into the final product — like a cake mix that still needs baking.
Technisch gezien: In materials processing, a precursor is an intermediate compound manufactured to a controlled specification and intended as the direct feed for a subsequent reaction that yields the end product. In lithium-ion battery supply chains the term most commonly refers to precursor cathode active material (PCAM) — typically a co-precipitated mixed hydroxide of nickel, manganese, and cobalt — which is blended with a lithium source and calcined to produce cathode active material. Confusion arises because 'precursor' is used across many industries with slightly different scopes; the battery-industry sense is narrower and more chemically specific than the general industrial usage.
Processing
pyrometallurgy
Extracting or refining metals using very high heat — think of a furnace hot enough to melt rock — to separate the metal from everything else.
Technisch gezien: Pyrometallurgy covers the high-temperature processing operations — including smelting, roasting, calcination, sintering and converting — used to extract metals from ores or concentrates and to refine crude metal. Reactions occur in solid, liquid or gas phases at temperatures typically ranging from a few hundred to well over a thousand degrees Celsius. The approach contrasts with hydrometallurgy in that separation relies on differences in melting points, oxidation potentials and slag–matte–metal phase equilibria rather than on aqueous chemistry; in practice many industrial flowsheets use pyrometallurgical and hydrometallurgical stages in series.
Processing
roasting
Heating ore in air at high temperature to cause a chemical reaction — most often turning sulfur compounds into gases and leaving behind a solid that is easier to process.
Technisch gezien: Roasting is a pyrometallurgical operation in which finely divided ore or concentrate is heated in a controlled atmosphere, most commonly air or oxygen, to achieve a specific chemical transformation of the solid feed — classically the oxidation of metal sulfides to oxides and sulfur dioxide. Unlike calcination, roasting is defined by the intentional reaction between the solid and the furnace atmosphere rather than simple decomposition. Several variants exist: oxidising, sulfating, magnetising and chloridising roast each target a different product phase, and the distinction between them is operationally significant when selecting downstream leach or smelting conditions.
Processing
sintering
Heating small particles of material until they just start to stick together and fuse at the edges, making a stronger solid without fully melting them.
Technisch gezien: Sintering is the thermal bonding of particulate material at temperatures below the bulk melting point, driven by diffusion across particle contact surfaces and the resulting reduction in surface energy. In iron and base-metal processing it is used to agglomerate fine ore or concentrate into a porous, mechanically stable burden suitable for blast or shaft furnace charging. The term is also applied in powder metallurgy and ceramics manufacturing, where the same physical mechanism produces dense, near-net-shape components; in those contexts it is sometimes confused with hot pressing, which additionally applies mechanical load.
Processing
slag
The stony waste left over after smelting. When metal melts away from rock, the leftover rocky material floats on top and is poured off separately.
Technisch gezien: Slag is the silicate-dominated, non-metallic waste melt generated during smelting or converting, formed when fluxes such as silica or limestone react with gangue oxides and iron oxides at furnace temperature. It is tapped separately from the metal or matte phase because of its lower density and, once solidified, is discarded or used as construction aggregate depending on its chemistry. Slags always contain some residual metal values either dissolved or as mechanically entrapped droplets, and their management—including re-processing of high-metal slags—is a standard part of smelter operations.
Processing
smelting
Melting a mineral concentrate at very high temperatures, sometimes with added materials, so that metal separates from the remaining waste. It is like melting a mixture in a bowl until the metal sinks away from everything else.
Technisch gezien: Smelting is a high-temperature pyrometallurgical process in which a sulfide or oxide feed is reacted—typically with a flux and, for sulfides, with oxygen—to produce a crude metal or metal-bearing matte that separates by density from a waste silicate melt called slag. For copper sulfide concentrates the immediate product is matte rather than metal; for iron ore the product is pig iron. Smelting is frequently confused with melting: melting simply changes a substance from solid to liquid without chemical reaction, whereas smelting involves chemical reduction or oxidation that changes the composition of the material.
Processing
solvent extraction
A chemical trick for moving metal out of a watery liquid and into an oily liquid, and then back into a different watery liquid—each time making the metal more concentrated and purer.
Technisch gezien: Solvent extraction, also called liquid–liquid extraction, transfers a target metal from a dilute aqueous pregnant leach solution into an organic solvent containing a selective extractant reagent, concentrating the metal and separating it from impurities that remain in the aqueous raffinate. The loaded organic phase is then contacted with a strong aqueous strip solution, releasing the metal at high concentration into the strip liquor, which is fed to electrowinning. In copper production the paired process is routinely abbreviated SX-EW (solvent extraction–electrowinning); solvent extraction is the purification and concentration step, while electrowinning is the deposition step, and the two should not be conflated.
Processing
spheronisation
A manufacturing step that rolls irregular particles of material into small, smooth balls, a bit like rolling scraps of dough into beads, so they pack together neatly and behave consistently.
Technisch gezien: Spheronisation is a size-enlargement process in which irregularly shaped granules or extrudates are tumbled at speed against a rotating friction plate, reshaping them into near-spherical pellets of controlled diameter and density. In battery-anode manufacture it is applied to graphite to improve packing density and electrolyte contact; in pharmaceutical processing it produces pellets of uniform flow and dissolution characteristics. The term is sometimes loosely applied to any pelletising step, but strictly it refers to the rounding of already-formed granules rather than the agglomeration of fine powder.
Processing
sponge metal
A lumpy, porous form of a pure metal produced straight from a chemical reaction — it looks a bit like a sponge because gas escaped while it was forming, leaving small holes throughout.
Technisch gezien: Sponge metal is the porous, irregularly structured form of a metal obtained by reducing a metal halide or oxide at high temperature without fully melting the product, leaving a solid mass riddled with interconnected voids where the by-product gases or salts were generated and escaped. Titanium sponge, produced by the Kroll process from titanium tetrachloride, and zirconium sponge are the most commercially significant examples. The product must be crushed, blended, and either melted or compacted by powder-metallurgy routes before it can be used; its porous character makes it an intermediate rather than a finished metal, and its composition and particle-size distribution are the principal quality parameters reported in trade.
Processing
yellowcake
A dry, powdery solid — usually yellow or orange — made by extracting uranium from ore and drying it out. It is the form in which uranium leaves a mine before further processing.
Technisch gezien: Yellowcake is the conventional name for partially refined uranium oxide concentrate, principally triuranium octoxide (U₃O₈) or ammonium diuranate depending on the precipitation process used, produced at or near a uranium mine by leaching ore, purifying the resulting solution, precipitating the uranium, and drying the solids. It represents the first saleable product in the nuclear fuel cycle and the standard unit in which uranium is traded and reported. The colour ranges from yellow to orange to dark brown depending on the drying temperature and chemical composition, so the name is not always literally accurate; the term persists as a recognised commercial and regulatory designation rather than a precise chemical description.
Processing