Bromine (\(\text{Br}\)) is a chemical element classified as a halogen, belonging to Group 17 of the periodic table. It is the only non-metallic element that exists as a liquid at standard room temperature, appearing as a dense, dark reddish-brown substance. Because of its high reactivity, it is highly corrosive and readily evaporates into a similarly colored vapor that has a pungent, irritating odor. This volatility and reactivity make bromine a valuable raw material in industrial chemistry, used to produce flame retardants, specialized drilling fluids, and intermediates for pharmaceuticals.
Primary Natural Sources
Bromine is not found in nature as the elemental liquid but rather as dissolved ionic compounds called bromides, such as magnesium bromide (\(\text{MgBr}_2\)) and sodium bromide (\(\text{NaBr}\)). Commercial quantities of these bromide salts are found highly concentrated in deep underground brine deposits. These concentrated brines are a primary source of extraction, with viable operations often found in locations like Arkansas in the United States.
Salt lakes, such as the Dead Sea, also host extremely high concentrations of bromide ions that are economically recoverable. Seawater, however, has a relatively low concentration of about 65 parts per million (ppm) of bromine, making its direct extraction less common than from concentrated brine or salt lake sources today. Commercial exploitation requires a high concentration of bromide ions to justify the energy-intensive extraction process.
Industrial Extraction Methods
The industrial process of “making” bromine is a chemical separation where the bromide ion (\(\text{Br}^-\)) is oxidized to liberate the elemental bromine molecule (\(\text{Br}_2\)). This is achieved using the “blowing-out” method, which utilizes the oxidizing power of chlorine gas (\(\text{Cl}_2\)). The reaction is a displacement where the more reactive chlorine displaces the bromide ion: \(2\text{Br}^- + \text{Cl}_2 \rightarrow \text{Br}_2 + 2\text{Cl}^-\).
The process begins by pre-heating the bromide-rich brine and acidifying it to a low pH of about 2.5. This acidification prevents side reactions and suppresses the hydrolysis of the newly formed bromine. The hot, acidic brine is then fed into a tall reaction tower, where it flows downward. Simultaneously, chlorine gas and steam are injected into the bottom of the column and rise counter-current to the brine flow.
As the chlorine gas reacts with the bromide ions in the solution, elemental bromine is rapidly formed and immediately converted into a vapor by the injected steam and the high operating temperature. This action, known as steam distillation or “blowing-out,” strips the liberated bromine vapor from the liquid brine solution. The resulting vapor stream, a mix of bromine, excess chlorine, and steam, exits the top of the reaction tower for purification.
Refining Bromine for Commercial Use
Once the bromine vapor is liberated from the brine, the subsequent steps focus on purification to achieve the high purity required for commercial applications. The mixed vapor stream is first cooled in a condenser, converting the gaseous bromine into a crude liquid form. This results in a two-phase mixture of liquid bromine and a bromide-rich aqueous solution.
The liquid is then passed through a gravity separator, or decanter, to separate the dense, crude liquid bromine from the lighter aqueous phase. The crude bromine still contains impurities, most notably residual chlorine gas and moisture. Excess chlorine is removed by treating the crude bromine with a reducing agent like sulfur dioxide, which reacts specifically with the chlorine.
Achieving anhydrous, or water-free, bromine is accomplished by drying the liquid, often by reacting the moisture with concentrated sulfuric acid (\(\text{H}_2\text{SO}_4\)). The final step is distillation, which involves heating the dried liquid bromine to its boiling point of \(58.8^{\circ}\text{C}\). This distillation removes any remaining non-volatile impurities and ensures the product meets the strict quality standards of over 99.9% purity before packaging.