Ural Federal University: University Scientists Found Out How to Efficiently Extract Silver

Chemists at Ural Federal University have identified the best sorbent based on aminopolymers modified with sulfoethyl groups for the extraction of silver ions from multicomponent solutions. The results of the research lead to the production of sorbents for the extraction of metals which concentration in solutions is insignificant. The obtained sorbents are potentially applicable, for example, in the purification of natural drinking water, fish ponds, in the processing of industrial waste. The research was supported financially by the Russian Science Foundation (grant № 21-73-00052) and is described in a scientific article published in the Russian Journal of Inorganic Chemistry.

“Sorption of metal ions is facilitated by the very nature of the aminopolymer matrix of the sorbents. Adding sulfoethyl groups to it, as our studies show, leads to a significant increase in the selective properties of sorbents that is the ability to absorb only certain ions from a wide set of different ions. The higher the degree of modification of sorbents by sulfoethyl groups, i.e. the more sulfoethyl groups in their composition, the better their selective properties. This particular work is dedicated to studying the extraction rate of silver ions from multicomponent solutions in the presence of copper, nickel, cobalt, zinc, and several other metals,” says Yulia Petrova, Head of the research group and Associate Professor at the Department of Analytical and Environmental Chemistry at UrFU.

Scientists tested four powdery sorbents based on aminopolymers with different degrees of modification by sulfoethyl groups namely chitosan, polyallilamine, polyethylenimine, and polyaminostyrol. They were synthesized by colleagues from the Laboratory of Organic Materials of the Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences.

First, the sorbents were placed in buffer solutions with a particular value of acidity. Analysis of the solutions after sorption made it possible to determine, firstly, the pH values corresponding to the highest selectivity of silver sorption by each of the studied materials. Secondly, it is shown that copper ions more than other metals interfere with the sorption of silver.

Thirdly, sulfoethylated polyallylamine has the highest selectivity of silver sorption and sulfoethylated polyaminostyrol has the highest rate of sorption. In this case, in the case of polyallylamine-based sorbent even copper is unable to seriously interfere with the sorption process: its initial rate and, as a consequence, the concentration of sorbed silver ions in the sorbent remain as high as possible.

Chitosan is productive in the sorption of both silver and copper, and the higher the degree of modification of chitosan with sulfoethyl groups, the higher the selectivity of silver sorption. Polyethyleneimine, depending on the acidity of the solution, is applicable both for joint sorption of silver and copper and for group extraction of other metals.

“The results of our research allow us to choose the most effective sorbent for certain tasks, depending on the degree of sulfoethyl group modification of sorbents, the acidity of the solution, the concentration of metals, the sorption rate. This opens up opportunities to create materials with specified properties, to extract various metals even from such solutions in which the content of these metals is insignificant,” explains Yulia Petrova.

Previous research of UrFU chemists was dedicated to the sorption of such noble metals as gold, platinum, and palladium. Development of methods to concentrate silver is an important task, not only because it is a precious metal, but also because silver is considered to be a potentially toxic element, while its concentration in many objects is extremely low.