Siberian Federal University

Palladium is a precious silver—white metal, which belongs to the platinum group metals along with rhodium, iridium, platinum, ruthenium and osmium. Today palladium is widely used in industry due to a special combination of its physical and chemical properties: good ductility and malleability, low melting point, hardness and rolling ability. All this makes palladium an important component of metal alloys — in particular, the alloy of gold with palladium (white gold). Due to its resistance to oxidation, the metal is used in electronics and medicine for the manufacture of instruments and prosthetics. Also there are cytostatic preparations based on palladium compounds for cancer treatment. Afterburning catalysts are made from palladium (in this process, fuel particles trapped in exhaust gases are eliminated), which are installed in cars to reduce harmful emissions into the atmosphere. Palladium is also one of the most common catalysts in petrochemistry. It has unique property of absorbing hydrogen — up to 900 volumes per volume of metal, therefore it is widely used for hydrogen storage and is the basis of hydrogen energy.

Palladium is rare in its relatively "pure" native form. In Russia, it is most often obtained from sulfide copper-nickel ores, where the metal is contained as a concomitant.

"Due to the expansion of the use of palladium in various fields of science and technology, the task of determining a low palladium content against the background of a high content of other related elements is relevant, since palladium is contained in ores at the level of 10-4%. Modern spectroscopic methods do not allow to determine palladium directly in these samples — there is not enough sensitivity. And another obstacle is the interfering influence of the matrix components of the ore, especially iron, the amount of which is tens of thousands of times more in the studied samples than palladium. We dissolve the ore and concentrates in acid mixtures and then use our sorbent to isolate only palladium from the solution. Thus, we concentrate it and eliminate the interfering influence of the main components of the studied samples," said Elena Borodina, co-author of the study, senior researcher at the research engineering center "Crystal" of Siberian Federal University.

The basis of the sorbent synthesized by scientists is silicon oxide (silica). One of the advantages of silica is its accessibility and the ability to give it various properties (specific surface area, porosity, grain size). However, silica itself as a sorbent is not very effective, and even more so it is not selective. To make it more "sensitive" to palladium, the researchers fixed special chemical groups on the surface of the grains that interact exclusively in acidic environments only with palladium and gold. The approbation was carried out using ores and products of their technological processing by Norilsk Nickel, located in the north of Krasnoyarsk Territory.

"Gold is also extracted together with palladium, but there is little gold in the Norilsk ores, so it does not interfere with the sorption and determination of palladium. It is also possible to develop a technique for isolating and determining gold using the same sorbent, but this is a topic for another study," clarified Elena Borodina.

According to the scientist, sulfur-containing groups help to give a narrow "specialization" to silica, which are fixed to the surface of silica by means of a chemical reaction.

"Special modifier substances, which are organosilicon compounds, contain, on the one hand, a functional group interacting with palladium ions, and on the other, an anchor silicon—containing group interacting with the surface of silica. Many modifiers are manufactured industrially, in particular, in Russia and China," the researcher said.

Such a sorbent looks like an ordinary white powder. It is not intended for the industrial production of palladium, but for determining palladium in technological samples in production laboratories.

The researchers note that the white colour of the sorbent allows it to be used for rapid tests. For example, to find out in the first approximation how much of palladium is contained in the solution. The fact is that the palladium compound, which settles on the surface of the sorbent, has an intense orange colour. You can take several portions of the sorbent and "plant" different amounts of palladium on it. You will get a scale in which the orange colour of the sorbent becomes brighter the more palladium is contained in the solution. After contact of the solution with the sorbent, you can compare the resulting colour with the colour scale and, according to the degree of "orange" colouration, give a preliminary assessment of how much of the valuable metal can be extracted from the solution.

"When the production process is underway, it is necessary to determine the palladium content at various stages — both in the feedstock, in intermediates, and in the final product. Palladium and gold are few, but there are many other components. With our sorbent, we separate only palladium. The sorbent is placed in a glass column with a diameter of 0.3 cm and a height of 8 cm. Then an industrial solution containing palladium is passed through the column. Palladium is extracted by the sorbent and can be "washed off" from it, and the sorbent can be reused (at least five times) to isolate palladium. The interfering components remain in the solution that has passed through the column. Palladium is completely "washed off" from the sorbent with a small amount of desorbing solution, and this solution is analyzed using an atomic emission spectrometer with inductively coupled plasma to establish the exact palladium content," explained Elena Borodina.

Very little sorbent is required for analysis, and from an environmental point of view it is practically safe, unlike the classical laboratory method of liquid extraction: they use organic solvents that pollute the environment, complicate working conditions and affect the health of employees performing the analysis. To study one sample of the solution and detect the desired metal in it, only 0.1 g of sorbent is required.

The scientists noted that they can currently produce an environmentally friendly sorbent directly on the basis of SibFU Scientific Research Engineering Center in laboratory batches. The prospects for practical use of the development are great. The sorbent can be used in analytical laboratories of Norilsk Nickel, Krasnoyarsk Plant of non-ferrous metals and gold, and others. The sorbent can also be useful in controlling organizations, such as the Customs, when it is necessary to analyze raw materials exported or imported into the Russian Federation.