The Newbery-Vautin chlorination process is a method for extracting gold from its ore through the use of chlorination. This process was jointly developed by James Cosmo Newbery and Claude Vautin.

Background
The process of extracting and reducing gold from pyrite in gold ores using chlorine gas was initially introduced by Karl Friedrich Plattner around 1848. This process was expected to revolutionize gold extraction; however, it required experienced chemists for successful execution.  

One drawback of the process was the presence of lime and magnesia in the quartz, as they would react with chlorine without yielding the desired results. Earthy particles would settle around the small gold particles, impeding chlorination. Additionally, other metals, such as lead or zinc, would be absorbed by the chlorine. Furthermore, the gold held in solution by the water could precipitate in the tailings before filtration was complete, resulting in the gold loss.   

Several individuals, including Henderson, Clark, De Lacy, Mears, and Deacon, introduced improvements to Plattner's process. However, these improvements often failed to cover all specific gold extraction cases. Lack of operator knowledge and the need for delicate chemical operations contributed to the failure of these processes. Consequently, plants utilizing these methods were rendered useless.

Claude Vautin, an experienced gold miner and extractor from Queensland, Australia, collaborated with James Cosmo Newbery, a government analytical chemist in Victoria. Together, they developed a process that aimed to overcome the challenges faced by previous methods and combine their advantages. By improving machinery and treatment techniques, they sought to facilitate the widespread adoption of the chlorination process.

Description
The treatment materials are placed in a revolving barrel hopper, which is constructed of iron and lined with wood and lead. It can withstand a pressure of 100 pounds per square inch and has a capacity of approximately 30 hundredweights (cwt) of ore. The charge from the hopper enters the chlorinator. Water and chlorine-producing chemicals, typically sulfuric acid and calcium chloride, are added. The manhole cover is then securely replaced to ensure a gas-tight seal. On the opposite side of the barrel, there is a valve connected to an air pump. The valve allows air to be pumped in at a pressure of up to four atmospheres to dissolve the generated chlorine gas. Once the valve is sealed, the barrel begins to rotate at a speed of about ten revolutions per minute, powered by a friction wheel. Depending on the ore's characteristics or the size of the gold grains, this rotation continues for a duration of one to four hours. During this time, the gold combines with the chlorine gas to form a soluble gold chloride, which is absorbed by the water inside the barrel. 

Afterward, the chlorinator is stopped, and the gas and compressed air are released through a valve connected to a rubber hose into a vat of lime water. This process neutralizes the chlorine to prevent the workers from inhaling any chlorine gas. The manhole cover is then removed, and the barrel resumes its rotation, causing the contents to automatically transfer into the filter positioned below. The filter is an iron vat lined with lead and equipped with a false bottom. A pipe connects the false bottom to a vacuum pump that operates intermittently. Once all the ore has been transferred from the chlorinator to the filter, the pump is activated, creating a partial vacuum beneath the false bottom. This results in rapid filtration. By this method, the gold chlorides present in the wet ore can be washed out as a continuous stream passes through the filter. The solution flowing from the filter is regularly tested, and when it is found to be free of gold, the water stream and vacuum pump are both stopped. The filter is then tilted, causing the contents to flow into a truck below, while the tailings are directed to a spoil tip. The washing and filtration process typically takes around an hour, during which another charge may be undergoing treatment in the chlorinator above. The filtered discharge and washings are collected in a vat and allowed to pass slowly through a tap into a charcoal filter. As the liquid passes through the charcoal, the gold in the gold chloride is reduced and deposited on the charcoal. Once the charcoal filter is fully charged, it is burned, and the resulting ashes are fused with borax in a crucible to obtain the gold.

Precursor Preparation 
In any chlorination system, it is necessary to remove sulfides from the ore. This is typically achieved through roasting using established methods. Roasting requires the careful and skilled application of heat, gradually increasing it. If the ore fuses due to neglect by the roaster, the charge is usually discarded as waste. This applies to both the Vautin process and other processes. The time required for treatment has significantly reduced, from thirty-six to ninety hours in older methods to three to six hours with highly satisfactory results. Previous processes involved careful dampening of the ore, aiming for the right moisture content. 

However, in the Newbery-Vautin method, damping is eliminated and water is poured into the barrel instead. The pressure applied, up to four atmospheres, allows chlorine gas to dissolve in the water, creating a strong chlorine solution. This solution permeates the ore, reaching the gold through every crevice. Chlorine gas also absorbs any silver associated with the gold. The rotary motion of the barrel prevents the accumulation of silver chloride around the gold grains, which would hinder gold absorption. The short contact time between the ore and chlorine prevents the formation of hydrochloric acid, which could prematurely precipitate the gold.

Filtration challenges, particularly with fine or slimy ore, were addressed with the introduction of the vacuum pump. The intermittent action of the pump creates a jigging motion in the filter, preventing clogging except in extreme cases of fineness.

The use of charcoal as a reducing agent for gold chloride was proposed by James Newbery many years ago. Although a patent was filed in the United States, the idea had been shared freely earlier, rendering the patent invalid. Previously, adding iron sulfate to the liquid from the filter precipitated not only gold but also lime and magnesia. Separating the gold from these required great care and a tedious process. With filtration through charcoal, everything soluble in hydrochloric acid is removed, including lime and magnesia, which previously caused complications. The chloride of gold is decomposed during passage through the charcoal, resulting in a purple film coating the gold particles.

If copper is present in the ore, the water, after passing through the charcoal filter, is directed over scrap iron. The copper precipitates due to a natural chemical reaction. If silver is present, it remains in the tailings as silver chloride, which is insoluble in water. In cases of significant silver quantities, leaching with hyposulfites can be employed.

One advantage of chlorination processes is the ability to treat dry-crushed ores, eliminating losses from float gold. Compared to mercury amalgamation, using chlorine gas does not require the ore to be finely crushed. Roasting replaces fine crushing as it alters the texture of the ore or causes flaws in silica grains, facilitating the penetration of chlorine gas into the gold.

Working with this improved process requires a chemist with knowledge, as is the case with any sophisticated process. The natural chemical reactions are not as delicate, but an inexperienced operator can still compromise the process. Newbery and Vautin extensively experimented with large ore samples from a mine before allowing the purchaser to implement their process. They adapt the formula until a practically perfect result is achieved, making it manageable for operators with moderate knowledge. Each mine's ore exhibits unique characteristics, and experiments begin with coarse crushing, gradually reducing them until the desired outcome is obtained.

To treat the entire ore body of a mine, dry crushing is recommended. An efficient stone breaker that reduces the ore to around ¼-inch cubes is necessary. Kroms rolls have proven to be satisfactory for subsequent crushing, producing an even texture to a thirty mesh size, which is usually sufficient. The crushed materials are then roasted in a reverberatory furnace and passed through the described machine. It is claimed that over 90% of the gold can be extracted using this method at a similar cost to other processes that were commonly used in gold-producing countries, which typically yielded only around 50%. 

Subsequently, the Newbery-Vautin process and other processes based on chlorination were replaced on processes based on cyanidation, which used less reagents. Still, more recently, processes that are free of cyanide and emit less toxic byproducts have also been developed.

References

Chemical processes
Metallurgical processes
Gold mining