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.
तकनीकी रूप से: 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.
तकनीकी रूप से: 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
haul road
The wide ramp-like road inside or outside a mine that large trucks use to carry ore or waste rock from the pit or tunnel to the surface.
तकनीकी रूप से: A purpose-built road within or adjacent to a mine workings, designed to carry heavy-duty haulage trucks — typically rigid-frame dump trucks of substantial capacity — between the working faces and the surface dump, stockpile, or processing plant. In open pit mines, haul roads spiral or switchback up the pit walls at a gradient constrained by the performance characteristics of loaded trucks. Road width, gradient, cross-fall, and surfacing are specified to suit vehicle size and traffic frequency. The haul road is a critical element of open pit geometry because its width and gradient directly affect the amount of waste rock that must be excavated to maintain access, influencing the strip ratio of the operation.
Mining
heap leaching
A process where crushed ore is piled into a large mound and a dissolving liquid is trickled through it; the liquid picks up the valuable metal and is then collected at the bottom for processing.
तकनीकी रूप से: A hydrometallurgical process in which run-of-mine or crushed ore is stacked in a prepared heap on an impermeable liner, and a lixiviant — typically dilute sulfuric acid for copper or a cyanide solution for gold — is applied to the surface and allowed to percolate downward, leaching soluble target metals into solution. The pregnant leach solution draining from the base of the heap is collected and processed to recover the metal. Heap leaching is distinguished from tank or vat leaching by its use of large unstirrred outdoor piles, which makes it suited to low-grade ores where the capital cost of finer grinding and agitated leaching would not be recovered; extraction efficiency is generally lower than with more intensive leaching methods.
Mining
heavy rare earth
The rare earth metals from the heavier end of the group — such as dysprosium, terbium and yttrium — which are rarer and harder to find in large deposits.
तकनीकी रूप से: Heavy rare earth elements (HREEs) are conventionally taken as gadolinium through lutetium, plus yttrium, distinguished by higher atomic numbers, greater ionic charge density and relative scarcity in most commercial ore bodies. They are enriched in ion-adsorption clay deposits and in monazite. HREEs tend to command higher prices than LREEs because workable concentrations are rarer and fewer deposits are in production; their supply is therefore considered more constrained. The same boundary ambiguity that affects the LREE definition applies here.
Materials
high-purity quartz
Sand or rock made almost entirely of the mineral quartz, with barely any other substances mixed in — so clean that it can be used to make the glass inside computer chips and solar panels.
तकनीकी रूप से: High-purity quartz refers to silicon dioxide (SiO₂) material in which the total concentration of impurity elements — including aluminium, titanium, iron, and alkali metals — has been reduced to the parts-per-million or parts-per-billion range through beneficiation and thermal or chemical purification. In practice it is distinguished from ordinary silica sand or quartz grit by its suitability for crucible and semiconductor-grade applications, where even trace impurities compromise crystal growth or optical transmission. The term is sometimes used loosely to include any washed silica, but technically it implies verified chemical analysis meeting the thresholds specified by downstream processors.
Materials
host rock
The body of ordinary rock that surrounds or contains a mineral deposit — the background rock that the ore or veins sit inside.
तकनीकी रूप से: Host rock is the pre-existing rock body within which mineralisation has been emplaced, precipitated, or formed, irrespective of whether that rock was chemically altered in the process. The term is descriptive and spatial rather than genetic: it identifies what the deposit is hosted in without implying a particular origin for the mineralisation. In metasomatic systems such as skarns, the host rock is substantially modified, while in many vein systems it may be largely unchanged; both usages are correct, and care is needed not to conflate 'host rock' with 'unaltered country rock'.
Geology
hydrometallurgy
Extracting metals by dissolving the ore in liquid and then recovering the metal from that liquid, rather than by melting anything.
तकनीकी रूप से: 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
hydrothermal
Anything to do with hot water moving through cracks in the Earth's crust, often carrying dissolved metals that crystallise out when the water cools.
तकनीकी रूप से: In economic geology, 'hydrothermal' describes processes, fluids, and deposits formed by the circulation of heated aqueous solutions through fractures and permeable zones in the crust. These fluids may derive from magmatic, metamorphic, or meteoric sources, and deposit minerals as temperature, pressure, or chemistry changes along the flow path. The term covers a wide range of deposit styles — from high-temperature porphyry systems to low-temperature epithermal veins — so it should always be qualified by temperature regime or deposit type in technical usage.
Geology