Boron Oxides, Boric Acid, and Borates (2001)

Abstract Boron, the fifth element in the periodic table, does not occur in nature in its elemental form. Rather, boron combines with oxygen as a salt or ester of boric acid. There are more than 200 minerals that contain boric oxide but relatively few that are of commercial significance. In fact, three minerals represent almost 90% of the borates used by industry: borax, a sodium borate; ulexite, a sodium‐calcium borate; and colemanite, a calcium borate. These minerals are extracted in California and Turkey, and to a lesser extent in Argentina, Bolivia, Chile, Peru, and China. China and Russia also have some commercial production from magnesium borates and calcium borosilicates. These deposits furnish nearly all of the world's borate supply at this time. The discovery of significant deposits of borates in both North and South America in the mid‐nineteenth century and their subsequent development helped to lower the price and greatly increase global usage, particularly as a key ingredient in soaps and detergents. Early in the twentieth century, larger and higher grade deposits found first in Death Valley and then in the Mojave Desert also helped speed the rate of borate consumption. Another world‐class deposit was discovered in Turkey in the late 1960s, making that country a major world producer. Refined borates are usually sold on the basis of their B 2 O 3 content and defined by their water or hydration content; borax pentahydrate or “5 mol,” borax decahydrate or “10 mol,” and boric acid are the three most commonly sold borate products. United States–based Borax, and Etibank, the Turkish national mineral producer, supply approximately 90% of the borates and refined borate products worldwide. There is a large global market for borates because of their unique chemical properties and relative cost‐effectiveness. Today, borates are used in a wide variety of products and rpocesses; the major markets are for insulation fiberglass, textile fiberglass, detergents and bleaches, enamels and frits, and agricultural products. Borates are essential for imparting strength as well as heat‐ and impact‐resistance to glass and glass fibers. The element boron is also an essential micronutrient for plants. Thousands of everyday items, including contact lens solutions, barbecue charcoal, brake fluid, and kitchenware–all contain borates. Other developments include the increased usage of ulexite and colemanite in the manufacture of some insulation products, and expanding applications for borates as pest control products, fertilizers, herbicides, wood preservatives, and flame retardants. Boron, in trace amounts, is an essential micronutrient for plants. Although it has not yet been proved that humans need boron to live, there is almost universal agreement that boron is nutritionally important to maintain optimal human health. Studies indicate that people is a wide variety of cultures consume ∼1–3 mg of boron per day through a combination of foods and drinking water in their local diets. Nevertheless, boron has come under some scrutiny in the latest revisions of drinking‐water standards, and there has been some legislation proposed in Europe to limit the amount of borate in detergent formulations as a result. Possible health benefits and the safe health limits of boron in the human system are still undergoing intensive investigation. The oxides and oxyacids of boron as well as a variety of hydrated and anhydrous metal borates are discussed herein.