Asbestos is a group of naturally occurring fibrous silicate minerals belonging to the groups of serpentines or amphiboles. Asbestos was widely used during the 19th and 20th century until the 1970s when public recognition of the health hazards of asbestos dust led to outlawing in mainstream construction and fireproofing in most countries. Structurally, the asbestos of chrysotile type has a two layered system where the first sheet is composed of SiO4 tetrahedra organized in a pseudo hexagonal network and the second one is composed of MgO6 octahedra. For the asbestos of amphibole type, the structure is more closed and the chemical reactivity will not be the same.
At present, the consequences of asbestos molecules interactions with human tissues have been well documented. In fact, its carcinogenic nature has been explicated beyond doubt. Therefore, since much of asbestos used during the early years spanning to the late 1970s in the modernized world still exists, it is imperative that an approach that could inert asbestos be developed.
The development of a process for eradicating all types of asbestos waste is a real challenge. Fortunately, a recent publication has demonstrated that it is possible to treat compact asbestos waste with two thermochemical treatments. Indeed, the study also confirmed that the use of acid allows for the dissolution of the inorganic matrix of waste as well as the chrysotile fibers. Regrettably, the study did not give direction regarding the valorization of solutions obtained after the acid and alkaline treatments. To address this, a group of researchers from the Charles Gerhardt Institute Montpellier at University of Montpellier, National School of Chemistry of Montpellier: Dr. Gael Talbi, Dr. Martine Cambon and Professor Olivier Cambon; proposed a complete recycling process of asbestos-containing industrial waste. Their work is patented and is currently published in Journal of Material Cycles and Waste Management.
In a nutshell, their approach entailed; first, the characterization of a friable waste to determine what kind of asbestos was present in the waste. Next, the researchers concentrated on the destruction of waste in optimal conditions so as to limit the loss of energy. To be precise, the chrysotile-containing wastes were treated with nitric acid solution leading to the generation of pure silica and an acidic solution. Alkaline treatment using sodium hydroxide was also used in the case of waste-containing amphiboles.
Essentially, a basic solution of silica was obtained. All in all, the researchers then proposed a first valorization route which entailed precipitation of the ions dissolved in the acid solution and a second with the synthesis of a zeolite using the solid silica resulting from the acid treatment and the solution coming from the alkaline treatment of the amphiboles as sources of silicon.
In summary, the study demonstrated that nitric acid treatment was able to destroy the structure of the serpentine-type asbestos (chrysotile), in their pure form or inserted in different type of inorganic waste. Remarkably, the approach allows for the destruction of wastes of high density having a low fiber content (roof tile and pipe seal) but also the low-density waste with a high fiber content (flocking). Better still, from waste containing chrysotile, pure silica powder with fibers and aggregates were obtained. Overall, Professor O. Cambon and colleagues described a virtuous cycle for destroying hazardous materials like asbestos and by transforming them towards materials with added value.
G. Talbi, M. Cambon, O. Cambon. Virtuous cycle of destruction and total recycling of pure asbestos and asbestos-containing waste. Journal of Material Cycles and Waste Management (2019) volume 21: page 1167–1176.Go To Journal of Material Cycles and Waste Management (2019)
G. Talbi, O.Cambon, M. Cambon. Asbestos waste destruction and valorization method. International Patent: WO/2019/038502, 28.02.2019.