Where in the future mankind is going to extract minerals
Authorities in Florida last week eliminated the threat of a dam breach protecting the village of Piney Point (near Tampa) from the liquid tailings of a bankrupt and inactive chemical plant. Had things gone wrong, nearly the entire contents of the huge man-made reservoir could have spilled onto nearby homes. Forpost decided to find out if industrial waste could turn from a threat to society into an additional tool for social and economic development.
Coal mining, non-ferrous and ferrous metallurgy, chemical and agrochemical plants are not only the backbone of the economy of any industrialized state, including Russia but also industries that produce a huge number of by-products. The most interesting thing is that the vast majority of them are real “gold mountains”, which at the current level of technology development can without exaggeration enrich those who will take up their development.
These are no longer off-balance ores, as they were called in the days of the Soviet Union or liquid tailings, but real technogenic deposits. For example, scandium and other rare-earth metals can be extracted from the red mud (pictured above) formed during bauxite processing. Calcium carbonate (phosphomel) and ammonium sulfate can be extracted from phosphogypsum, a byproduct of the processing of phosphate rock (phosphate rock and apatite, used for fertilizers).
“Calcium carbonate can be used, for example, for liming of soils, its use allows increasing the yield, which is especially important for regions with a humid climate, such as the Northwest of Russia. The fact is that precipitation increases the acidity of the soil, and phosphomel brings it to the normative values. Besides, it is in demand in the production of steel and Portland cement. Well, and ammonium sulfate is a mineral nitrogen fertilizer that is in high demand. It dissolves well in water, is not washed out even by heavy rains and, most importantly, helps crops with fewer losses during temperature changes, drought or, conversely, high humidity,” says Vyacheslav Brichkin, the head of the Metallurgy Department of Saint Petersburg Mining University (Professor Victor Sizyakov was the scientific supervisor).
All over the world today about 170 million tons of phosphogypsum are produced annually. Part of it is used, for example, as a reclamation agent for reclamation of saline and disturbed agricultural lands. Or it could be used as an analog of sand in the construction of roadbeds. It is also used in the manufacture of a variety of binders, plasterboard, and other products.
Nevertheless, the existing demand does not allow to involve in the production of all the phosphogypsum, and it continues to accumulate. In order to solve this problem, the core business in different countries of the world involves scientists, who in the course of scientific experiments look for cost-effective options to develop these technogenic deposits and extract useful components from them.
In Russia, the industrial exploitation of deposits of apatite, which has been called “the stone of fertility” for its unique properties that make it possible to produce fertilizers, started as early as 1929. That is when the first ton of the valuable raw material was lifted from the ground in the Khibiny (the largest mountain massif of the Kola Peninsula). No one thought about the need to dispose of waste at that time, but for PhosAgro, the current subsoil user, this is one of the priority tasks.
"To work on the creation of technology for conversion of phosphogypsum into crystalline products - ammonium sulfate and calcium carbonate, we involved St. Petersburg Mining University. Our choice was not accidental; cooperation with this university is a strategic area for the company. The Group's development program to 2025 was drawn up thanks to this partnership. Besides, thanks to the innovations proposed by scientists from Mining University, we were able to introduce modern instrumental methods to ensure the safety of mining operations and increase the efficiency of extraction of apatite-nepheline ores,” explained Boris Levin, Deputy Chief of Staff of PhosAgro's Chief Executive Officer.
The goal of the scientific team, which was involved in developing a way to utilize phosphogypsum as a secondary resource, was to create a pilot plant at the company's Cherepovets cluster site. This enterprise produces almost 4.5 million tons of phosphogypsum-containing fertilizers per year. The technology test was successful - all the theoretical conclusions related to the prospects of obtaining products in demand in the market were confirmed in practice.
“Technological testing was successful. We have designed a pilot line enabling us to continuously process 50 kg of phosphogypsum per hour. Thus, the expediency of building the plant, the capacity of which can reach 500 thousand tons per year, was fully justified from a scientific point of view. The process has been tested on a pilot plant with the simulation of each technological stage and the possibility of subsequent scaling,” said Vyacheslav Brichkin.
Calcium carbonate and ammonium sulfate are produced by treating phosphogypsum with ammonia or its compounds and carbon dioxide. That is, in the course of this procedure, CO2 emissions are also reduced. And Russia, according to official data, is the fourth-largest emitter of carbon dioxide in the world, and reducing this indicator is also an extremely important task.
“Together with scientists from Mining University, we studied in practice the physical and chemical parameters of each stage of the technology, developed design documentation for non-standard types of equipment. We confirmed high technological indicators of phosphogypsum conversion (at the level of 90% - editor's note) into target products. The work done creates the required groundwork to expand the use of this byproduct along with the areas of application that have already been tested in practice. I mean road construction, cement production, and so on," summarized Boris Levin.
Today scientific research in the field of phosphogypsum utilization is continuing at St. Petersburg University. In particular, the possibility of extracting rare-earth metals of light group, which content is from 0.5 to 1%, is being studied.