Amalgamation is the process of combining mercury with another metal to form a soft, workable alloy called an amalgam. Mercury’s unusual ability to dissolve metals at room temperature has made this technique valuable for thousands of years, from extracting precious metals out of crushed rock to filling cavities in teeth. The word itself has grown beyond chemistry into everyday language, where it means any blending of distinct parts into one, but the physical process behind it remains one of the most consequential interactions in metallurgy and public health.
What Happens When Mercury Meets Another Metal
Mercury is the only metal that stays liquid at room temperature. When it contacts gold, silver, tin, copper, or certain other metals, it creeps into the metal’s crystal structure and bonds with it, forming a new alloy. The resulting amalgam can range from a thick paste to a near-solid lump, depending on how much mercury is in the mix and which metal it has absorbed. This reaction does not require heat or special equipment, which is why amalgamation has been so appealing across centuries and cultures: you simply pour liquid mercury over ore, and it pulls the target metal out.
Not all metals amalgamate easily. Iron and platinum resist mercury, which is why steel trommels and iron pans have historically been used to hold the mercury during processing without being consumed by it. The selectivity of mercury for certain metals is the foundation of every practical application of amalgamation, from gold extraction in a riverbed to sensor technology in a modern laboratory.
Silver Mining and the Colonial Mercury Trade
The large-scale industrial use of amalgamation began in the Americas in the 1500s. With access to mercury from the cinnabar mines of Huancavelica in Peru, Spanish colonial operators adopted amalgamation to refine silver at Potosí, Bolivia, beginning in the early 1570s. The process was staggeringly mercury-intensive. Between 1564 and 1810, an estimated 17,000 metric tons of mercury vapor were emitted from cinnabar smelting at Huancavelica alone, and roughly 39,000 metric tons of mercury were released as vapor during silver refining operations at Potosí.1PubMed Central. Mercury production and use in colonial Andean silver production: emissions and health implications
Those numbers are enormous by any standard. The mercury was mixed with crushed silver ore in open-air patios, and because the amalgam had to be heated to drive off the mercury and recover pure silver, vast clouds of mercury vapor rose over the refining sites for centuries. Workers, many of them indigenous people under forced-labor systems, were exposed at levels that would be unthinkable by modern occupational standards. This colonial chapter established a pattern that persists in modified form today: amalgamation is cheap, effective, and devastating when mercury is handled carelessly.
Artisanal Gold Mining Today
Amalgamation did not fade out with the colonial era. It remains the go-to method for millions of small-scale gold miners worldwide. In so-called whole-ore amalgamation, rocks are crushed to a coarse sand, loaded into motorized drums with water and heavy steel or tungsten balls, and then liquid mercury is added directly. A common ratio is about 0.3 to 1 kilogram of mercury for every 20 kilograms of crushed ore. The mercury captures fine gold particles that would otherwise be lost, forming dense amalgam balls that are typically 40 to 80 percent mercury by mass.2PubMed Central. The Mercury Problem in Artisanal and Small‐Scale Gold Mining
Miners then squeeze excess mercury out through cloth, a step that recovers some mercury for reuse but leaves plenty behind. Studies in Ecuador found that only about 51 to 59 percent of the mercury introduced into the process is recovered at this stage. Roughly 29 percent is lost when miners burn the amalgam to drive off mercury and obtain gold, and about 15 percent escapes with the tailings, the leftover crushed rock and water that wash into nearby streams. When whole ore rather than just gravity concentrates is amalgamated, nearly 30 percent of the mercury entering the system ends up in those tailings.3Journal of Cleaner Production. Mercury balance in amalgamation in artisanal and small-scale gold mining: identifying strategies for reducing environmental pollution in Portovelo-Zaruma, Ecuador
Artisanal and small-scale gold mining is now the single largest human-caused source of mercury emissions and releases into the environment. The amount of mercury lost per unit of gold produced varies by region: estimates put the average ratio of mercury lost to gold produced at about 1.2 in Asia, 2.0 in Africa, and 4.6 in Latin America, with the differences largely explained by whether miners amalgamate the whole ore or just a gravity concentrate.4Journal of Sustainable Metallurgy. Estimation of Mercury Losses and Gold Production by Artisanal and Small-Scale Gold Mining (ASGM) Latin America’s heavy reliance on whole-ore amalgamation drives those particularly high losses.
What Mercury Amalgamation Does to Ecosystems
The mercury that escapes during amalgamation does not simply vanish. In waterways near mining sites, sediments accumulate high concentrations of both total mercury and methylmercury, the organic form that is far more toxic and bioavailable. Research along the Gambia River in Senegal, where artisanal gold mining has expanded, found elevated mercury and methylmercury in sediment samples collected at mining sites. An unsettling pattern emerged: while total mercury in sediment dropped with distance downstream, methylmercury actually increased, because fine mercury-laden particles settling downstream create favorable conditions for bacteria to convert inorganic mercury into its methylated form.5PubMed. Impact of recent artisanal small-scale gold mining in Senegal: Mercury and methylmercury contamination of terrestrial and aquatic ecosystems
Methylmercury biomagnifies up the food chain: small organisms absorb it, fish eat those organisms, and predators at the top of the chain, including people who eat the fish, accumulate the highest concentrations. Surface soil erosion can also carry mercury from old mining sites into aquatic ecosystems years after mining has stopped, meaning the contamination is not just an acute problem but a long-term one that outlasts the mining activity itself.
Health Risks for Miners and Their Communities
The step that poses the greatest danger is burning the amalgam. To separate gold from the amalgam ball, miners typically heat it over an open flame or a simple stove, vaporizing the mercury so that a purer gold nugget remains. This produces dense mercury vapor in and around the workspace. In a study of a gold mining community in Ghana, about 91 percent of households where amalgam burning was reported had indoor mercury vapor concentrations above the U.S. EPA reference level, and in some cases concentrations at fireplaces exceeded the upper measurement limit of the instruments.6PubMed. Human health risk assessment of exposure to indoor mercury vapour in a Ghanaian artisanal small-scale gold mining community Even households where amalgam burning was not reported showed elevated mercury levels, with roughly 64 percent exceeding the EPA reference dose, suggesting that vapor drifts widely through these communities.
The health consequences are primarily neurological. Reviews of health studies across artisanal mining communities consistently report tremor, coordination problems, memory impairment, and vision disorders among workers who handle amalgam. These effects extend beyond miners to people who live downstream and eat mercury-contaminated fish.7PubMed Central. Mercury Exposure and Health Impacts among Individuals in the Artisanal and Small-Scale Gold Mining Community: A Comprehensive Review In Colombia, miners who burned amalgams had mercury concentrations in blood, urine, and hair roughly seven to eight times higher than miners who did not, with burning amalgam and fish consumption both identified as significant predictors of exposure.8PubMed. Occupational human exposure to mercury in artisanal small-scale gold mining communities of Colombia
Alternatives That Could Replace Mercury in Mining
If amalgamation is so harmful, why do millions of miners still use it? The answer is cost, simplicity, and habit. Mercury is cheap, requires no electricity, and the technique can be learned in an afternoon. Alternatives exist, but getting them adopted is a different challenge.
Borax smelting is one of the most promising substitutes. Instead of using mercury, miners concentrate their ore through gravity separation and then smelt the concentrate with borax, a common and inexpensive mineral, which lowers the melting point and helps gold separate from slag. A study comparing the two methods on ore samples from western Ethiopia found that borax smelting produced a mean gold recovery of about 0.61 grams per sample compared to 0.23 grams with mercury amalgamation, more than doubling the yield while eliminating mercury entirely.9International Journal of Innovative Science and Research Technology. Evaluation of Borax as an Alternative to Mercury in Gold Recovery: A Case Study of Benishangul Gumuz Region, Assosa Area, Western Ethiopia A separate comparison in Uganda found that direct smelting recovered about 40 percent more gold than amalgamation, took only marginally longer, and used no mercury at all.10PubMed Central. Comparison of Gold Yield with Traditional Amalgamation and Direct Smelting in Artisanal Small-Scale Gold Mining in Uganda
These results are striking because they undercut the assumption that mercury amalgamation gives miners the best return on their effort. The barrier to adoption is not performance but infrastructure and training. Borax smelting requires a crucible and a heat source capable of reaching higher temperatures, and miners need to be taught the gravity-concentration steps that precede it. International programs have been running training workshops for years, with mixed uptake.
Policy Efforts and the Minamata Convention
The Minamata Convention on Mercury, which entered into force in 2017, is the major international agreement aimed at reducing mercury use globally. Countries where artisanal mining is significant are required to develop national action plans to curb mercury use. In practice, progress has been uneven. Many countries in which artisanal mining is practiced have ratified the convention, but few have actually submitted their national action plans or enforced specific laws to restrict mercury in mining. Analysis of mercury trade data suggests that in 2017, direct trade in metallic mercury did decline in some African and Latin American countries, but new trade flows of products with higher mercury content emerged, potentially circumventing the restrictions.11Resources, Conservation and Recycling. Examining the inconsistency of mercury flow in post-Minamata Convention global trade concerning artisanal and small-scale gold mining activity
The challenge is familiar to anyone who follows environmental policy: demand-side reduction is extremely difficult when millions of livelihoods depend on the existing process and enforcement infrastructure is thin. Banning mercury without providing workable alternatives and economic support can push the trade underground rather than eliminate it.
Dental Amalgam, the Most Familiar Amalgam
For most people in industrialized countries, the word “amalgam” brings to mind the silver-colored fillings that dentists have placed in teeth for more than 150 years.12PubMed. High mercury emissions from dental clinics despite amalgam separators Dental amalgam is a mixture of mercury with a powder of silver, tin, copper, and sometimes other metals. When freshly mixed, the amalgam is soft enough to pack into a prepared cavity, then it hardens over a few hours into a durable filling that can withstand decades of chewing forces.
The safety of dental amalgam has been debated for as long as it has existed. The core concern is that mercury is continuously released at low levels from the surface of the filling, especially during chewing. One analysis estimated that the absorbed dose from a typical number of fillings is on the order of 1 to 3 micrograms per day. To put that in perspective, the same analysis calculated that roughly 450 to 530 amalgam filling surfaces would be needed to produce urine mercury levels associated with even the most subtle pre-clinical health effects in the most sensitive individuals.13PubMed. Mercury exposure from dental amalgam fillings: absorbed dose and the potential for adverse health effects Since few people have more than a couple dozen filling surfaces, that is an enormous safety margin.
Reviews of the topic generally conclude that the mercury released from set amalgam fillings is far below current health standards, and that the main exposure window occurs during placement or removal of the filling, not during the years it sits in the tooth.14PubMed Central. The dental amalgam toxicity fear: a myth or actuality That said, the picture is not entirely settled. Some researchers have argued that mercury vapor from dental amalgam is the predominant source of mercury in the central nervous system of adults in developed countries and that even low-level exposure poses risks during fetal and early childhood brain development, a concern supported by animal experiments and some occupational studies of pregnant women exposed to mercury vapor.15PubMed. Mercury in dental amalgam: a risk analysis This is a real disagreement in the literature, not a fringe concern, though mainstream dental organizations in most countries still consider amalgam safe for the general population.
Amalgam Versus Composite Fillings
Whether or not you find the mercury argument persuasive, dental amalgam is in decline. Tooth-colored composite resin fillings have steadily replaced amalgam in many countries, driven by patient preference for aesthetics and by regulatory phase-downs in some regions. The practical tradeoff is durability. Systematic reviews consistently find that amalgam fillings last longer on average than composite resins in the back teeth that take the heaviest chewing loads. The main reason amalgam fillings eventually fail is fracture, while the main reason composites fail is new decay forming at the margins of the filling.16PubMed Central. Longevity of Amalgam Versus Composite Resin Restorations in Permanent Posterior Teeth: A Systematic Review
Composites have improved substantially, though. A long-term follow-up study found that large composite restorations placed after removing old amalgam fillings showed good survival over a mean observation period of 15 years.17PubMed. Clinical longevity of extensive direct resin composite restorations after amalgam replacement with a mean follow-up of 15 years The gap between the two materials is narrowing as adhesive techniques and composite formulations improve, and for most patients today the choice between them hinges more on the size and location of the cavity and the dentist’s judgment than on any blanket superiority of one material.
Amalgamation in Geology
Geologists borrowed the word “amalgamation” long ago to describe the process by which separate landmasses collide and fuse into a single larger continent. The assembly of a supercontinent is, in a loose but apt metaphor, the Earth amalgamating its scattered crustal fragments.
Evidence from the Yilgarn craton in Western Australia records one such episode. Regardless of the individual ages and compositions of its various terranes, all of them show signs of intense tectonic, volcanic, and metamorphic activity between roughly 2,780 and 2,630 million years ago. This burst of activity is interpreted as a major episode of plate tectonics that swept together volcanic arcs, back-arc basins, and microcontinents into a supercontinent, of which the Yilgarn craton is a surviving fragment.18Geological Society, London, Special Publications. The generation and assembly of an Archaean supercontinent: evidence from the Yilgarn craton, Western Australia
Supercontinent amalgamation has consequences far beyond rearranging maps. The collision of landmasses builds enormous mountain belts, and the weathering of those fresh mountain ranges draws carbon dioxide out of the atmosphere. As a result, supercontinent assembly tends to coincide with climatic cooling on a global scale.19PubMed Central. The supercontinent cycle and Earth’s long-term climate The link between tectonic amalgamation and ice ages is one of the deeper connections in Earth science, tying the movements of plates hundreds of millions of years ago to the glacial episodes recorded in the rock record.
Amalgamation in Sensing and Laboratory Technology
Mercury’s eagerness to amalgamate with gold turns out to be useful for detecting mercury itself. When mercury vapor contacts a thin gold film, it absorbs into the film and changes its electrical resistance. This principle was demonstrated decades ago as the basis for a simple, fast mercury detector that requires no chemical separations beyond passing the sample through standard dry filters.20PubMed. Mercury detection by means of thin gold films The mercury-gold amalgam that forms on the film surface produces a measurable resistivity shift, and researchers have continued refining and validating models of this interaction for use in environmental monitoring.21Sensors and Actuators B: Chemical. Model validation of a mercury sensor, based on the resistivity variation of a thin gold film
Meanwhile, in chemistry laboratories, sodium amalgam, an alloy of sodium and mercury, serves as a mild and selective reducing agent. It can convert certain reactive chemical groups into others while leaving a wide range of sensitive structures intact, a selectivity that makes it valuable in organic synthesis even though the broader trend in chemistry is to minimize mercury use.22Chinese Journal of Chemistry. Sodium Amalgam, a Useful Reducing Reagent for Formation of Amines from Azides Bearing a Variety of Functional Groups
Gallium Alloys and the Push to Replace Mercury Everywhere
The same properties that make mercury useful, liquid at room temperature, wets metal surfaces, transmits pressure, also make it hazardous. A growing body of work focuses on gallium-based liquid metal alloys, particularly the eutectic blend of gallium, indium, and tin known commercially as Galinstan, as a nontoxic substitute. Galinstan is already familiar from mercury-free thermometers, but its applications are expanding. Researchers have demonstrated that it works as a sealing and pressure-transmission fluid in phase-equilibrium cells, performing well especially at high temperatures where mercury has traditionally been the default choice.23Journal of Chemical & Engineering Data. Application of GaInSn Liquid Metal Alloy Replacing Mercury in a Phase Equilibrium Cell: Vapor Pressures of Toluene, Hexylbenzene, and 2-Ethylnaphthalene
One of the more ambitious applications is replacing mercury in porosimetry, the measurement of pore sizes in solid materials. Mercury intrusion porosimetry has been a standard technique for decades, but it generates hazardous waste with every run. Systematic studies have shown that Galinstan can be pushed into porous materials and withdrawn in a controlled way that yields useful data on pore structure, offering the first realistic prospect of removing mercury from this widely used analytical method.24PubMed. A Nonhazardous Alternative to Mercury in Liquid Intrusion Porosimetry: Systematic Study of Intrusion/Extrusion Behavior of a Gallium-Based Liquid Metal (eGaInSn) into Meso- and Macroporous Silica, Alumina, and Carbon Materials Gallium alloys do not amalgamate with gold and silver the way mercury does, so they cannot simply slot into gold mining. But for the many laboratory and industrial roles where mercury’s value was its liquid state and nothing more, the replacement is well underway.