Boron in Metals and Gold


Borates have a wealth of uses in metallurgy and gold refinement. Aside from specialized uses such as the production of super strong magnets, borates:

  • Make excellent fluxes, used to remove oxide impurities from metals including gold
  • Are added to steel and aluminum to produce hard, corrosion-resistant alloys
  • Are used to stabilize metallurgical slags and divert them from landfills
  • Passivate ferrous and other metal surfaces to reduce their susceptibility to corrosion
These capabilities make borates an invaluable component in the production of jewelry, wiring, automobiles, water-treatment facilities, and wind turbine engines.

Borates in metallurgy

Borates are used in the production of steel and non-ferrous metals, alloys, rare earth magnets, amorphous metals, welding fluxes, and plating compounds.


Use of borates in metallurgy begins at the beginning—with the mining process itself. In copper mining, 20 Mule Team® Borax ammonium pentaborate solutions are used to stabilize blasting holes.

In the production of steel and non-ferrous metals, borates act as a flux during smelting. In this capacity, they are used to dissolve metallic oxide impurities, which are then removed with the slag. Borates are also used as a cover flux, to provide a protective barrier against air oxidation. Optibor® and 20 Mule Team Borax potassium pentaborate is used in fluxes for stainless steel or various non-ferrous metals to avoid the glare that is associated with sodium borate. In the refinement of copper, copper alloys, and precious metals, potassium pentaborate can be used as an alternative to fluorine-containing flux compounds, thus helping to reduce fluorine emissions.

In electroplating—including the electroplating of printed circuits—Optibor and fluoboric acids are used in plating solutions, electrolyte solutions, and as an intermediary.

As in metal refinement, in silver soldering, brazing, or welding, potassium pentaborate is used alone or in a mixture with other materials to create a flux that melts and dissolves oxide impurities on the metal surfaces to be joined. Almost all dry paste welding and brazing fluxes contain borates, to protect the surface of the metal against oxidation, act as a solvent in dissolving the metal oxides surrounding the areas to be joined, and serve as a detergent, removing oxides, grease, and other foreign matter.

Ferroboron is used in the production of bonded magnets and permanent magnet materials made with earth-iron alloys. And boron-containing, amorphous metal alloys are used to produce soft magnetic cores that can reduce energy loss in electrical transformers by up to 85%.


Borates readily associate with metallic oxide contaminants at a sufficiently low temperature to minimize the loss of precious metal and reduce wear and tear on melting equipment. In gold refinement, Dehybor® anhydrous borax is used in flux formulations to dissolve metal oxides and as a flux in gold assaying. The addition of Dehybor to the smelt is generally 10-50% of total smelt weight, depending on the process. The borax contribution to flux composition can be up to 60% of total flux weight but is typically around 30-40%.

Borates are also used to facilitate the attack of gold ore at a lower temperature and to make the slag more fluid at the furnace operating temperature, thus reducing viscosity. The benefits of Dehybor in gold refining are numerous:

  • Recover precious metal content with minimal loss to slag
  • Promote a substantial reduction in the sintering temperature of the charge
  • Produce easily fusible borates
  • Prevent combustibility and minimize fuming
  • Form highly fluid slags with only mild attack on refractories
  • Easily thickens slag if necessary and slammed
  • Avoid intumescence and puffing

Furthermore, the product’s formation, purity, and consistent granulometry make it the ideal product for preventing “spit and crackle” problems and facilitating the proper melt.

Slag stabilization

Most steel slags form hard, rock-like materials upon cooling, whereas others (especially those from the production of stainless steel) form dusty powders. These dusty slags can be prevented by adding anhydrous borax, creating a βC2S polymorph form that results in a stable, rock-like material. Benefits include less slag dust, easier handling of slag, reduction in regulatory oversight and improvement in community relations thanks to improved housekeeping practices, and revenue from sale able slag as well as savings on landfill taxes, disposal costs, and treatment costs.

For more information, download the brochure Borates in Steel Slag Stabilization (English) or (Chinese / 中文)

Borates in slag stabilization

Upon cooling, slags from some processes form weak rock-like material that slowly disintegrates, forming dust and mud—which is difficult to deal with. Adding a specialized borate to the molten slag has been shown to prevent these destructive density changes. The slag cools in a stable way, resulting in a slag off-take in the form of fist-sized rocks and minimal dust—and a safer, cleaner working environment. No mud, better handling, and no need for water cooling also typically mean a reduction in costs, thanks to lower energy consumption and easier disposal. And the rock-like slag makes a far more useful construction material.

Lead recycling and metals recovery

Recycling and recovery of metals such as brass, bronze, copper, lead, zinc, and aluminum can come from scrap or from slag that is left over from a primary smelting operation. The production of a product as pure as primary metal requires the removal of all oxides and extraneous impurities. Borates help by acting as fluxes during melting, combining with metallic oxides at relatively low temperatures to bring them to the surface of the melt as a slag that can be decanted or skimmed off.

In smelting of non-ferrous scrap, anhydrous borates such as Dehybor help to avoid the puffing and intumescence (with possible steam explosions) that can occur when hydrated borates are heated vigorously. Dehybor forms an excellent liquid flux for most bronzes, brasses, and similar alloys and serves as a scavenger to dissolve and carry out oxides, dirt, and sand, which so often contaminate non-ferrous scrap.

In the recovery of nickel, Optibor, 20 Mule Team Borax boric oxide, and Dehybor are used to maintain the neutral pH conditions that are necessary when dissolving impure nickel anodes. Borates are also used in the process of preparing bauxite ore for aluminum, as well as in refining gold and silver. In the latter, Dehybor readily associates with metallic oxide contaminants at a low enough temperature to minimize the loss of precious metal and to increase the longevity of the melting equipment.

In lead recycling and recovery, as with other metals, borates provide value in several ways:

  • A high solvent action on metal oxides and siliceous materials produces a purer metal.
  • The formation of highly fluid slags (due to the reduction of the liquidus temperature) enables the extraction of more lead.
  • Slags can be thickened and skimmed more easily, based on metal chemistry.
  • Energy costs are reduced, thanks to the lowering of the melting point in the furnace.
  • The cooled, more solidified slag should be improved through the reduction in the leaching effect of lead sulfate from the slag.
  • Inorganic borate compounds are easier and safer to handle than many alternatives.
  • Borates are non-combustibile, with minimum fuming tendency.

For more information about metals recovery and lead recycling using borates, download Borates in Lead Recycling (PDF).


Borates and bauxite ore

Borates are also used in the process of preparing bauxite ore for aluminum, as well as in refining gold and silver.

20 Mule Team Borax Products

These 20 Mule Team Borax products are developed for use in metallurgy.

Ammonium Pentaborate

Whether inhibiting heat, flame, or corrosion, the purity of this alkaline salt makes it an excellent choice. Learn More

Borax Decahydrate

From detergents to dyes to adhesives, this mild alkaline salt does it all, particularly excelling as a buffering and fluxing agent. Learn More

Boric Oxide

Pure anhydrous form is ideal where boric acid is required without metals. A powerful tool in the production of specialty glasses, ceramics, enamels, and fluxes. Learn More


This hard, glassy, granular product is excellent when forming flux or glass, where it helps to increase yield and reduce energy consumption. Learn More


With lower transportation, handling, and storage costs, this concentrated sodium borate is used in glass, fiberglass, cleaning products, and flame retardants. Learn More

Optibor boric acid

From reducing melting temperatures in fiberglass production to inhibiting corrosion in fuel additives, Optibor has a multitude of uses in numerous industries. Learn More

Potassium Pentaborate

Unique capabilities make it ideal for the automotive industry, where its addition to gear lubricants improve load-carrying capacity and wear protection. Learn More

Potassium Tetraborate

An excellent buffering agent, potassium tetraborate can lower the pH of strong alkalis and is also used in welding, soldering, and brazing fluxes. Learn More


When it comes to particulate materials, particle size affects end product quality and properties. U.S. Borax offers many of its products in powder grade. Learn More

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U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 500 customers with more than 1,700 delivery locations globally. We supply 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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