Possessing high strength, low density and significant chemical resistance, titanium has found wide application in various fields of the national economy – the chemical industry, aviation and rocket technology, mechanical engineering, medicine, etc. The production of titanium products is hampered by a fairly strong oxide film covering its surface. Removal of the oxide film from the surface of titanium workpieces is carried out by etching in solutions of mineral acids of various compositions. A spent acid etching solution (SAES) is formed, containing titanium salt and the remainder of unreacted acids. Almost all etching solutions contain HF and one of the strong acids. This is H2SO4, HCl or HNO3. Thus, the SAES includes ions of titanium, fluorine or chlorine, orsulfate, or nitrate. SAES is quite toxic and must be diluted or cleaned several times before being discharged into a reservoir. Most of the methods used to extract impurities contained in SAES lead to a decrease in their content. As a result of such purification, there is a loss of substances contained in SAES in significant quantities and of interest for further use. The work presents experimental results obtained from the combined processing of SAES containing titanium fluoride, hydrofluoric and hydrochloric acids. At the first stage, SAES is treated with sodium hydroxide. The resulting titanium hydroxide precipitate is filtered off. At the second stage, the filtrate containing sodium fluoride and chloride is processed in a membrane electrolyzer. In this case, not only the extraction of sodium salts from the filtrate occurs, but also the production of sodium hydroxide and a mixture of hydrofluoric and hydrochloric acids. Sodium hydroxide can be used for processing SAES, and a mixture of acids for etching titanium workpieces.
The scale of land pollution with oil waste necessitates the use of economical and effective methods of recultivation. Phytoremediation is one of the simplest methods, but it has a number of limitations, so additional preparation of the territory is often required before it is carried out. Preliminary electrical preparation and subsequent seeding of special phytoremediants are of interest. Passing a constant electric current through the soil volume under a low voltage removes toxicants from deep soil layers even with flooding. In addition, it reduces pollutant content in the upper layer, where the plants root system is located, which creates more favorable conditions for phytoremediants. Adequately selected types of plants will ensure additional soil cleaning, improve its structure and air exchange. The results of two research directions are presented. Experiments on the study of plant resistance to oil-contaminated soil substrate allowed establishing contamination thresholds at which it is advisable to sow a particular species, and to choose optimal phytoremediants. The study of the oil-containing soil cleaning in a monocathodocentric electrochemical installation with the fixation of main characteristics (oil products concentration, soil temperature, volt-ampere characteristics) allows us to develop technical measures to prepare territories for phytoremediation taking into account the relief features.
Electrochemical cleaning of oil-contaminated soils is a promising area of environmental safety, as it can be easily organized even in locations remote from settlements. For this purpose, a power source and a system of electrodes are necessary as equipment. It is possible to use an electric generator if there are no power supply lines nearby. The material of electrodes affects the features of redox processes, which can affect the energy consumption and the degree of soil cleansing from oil or oil products. Therefore, the correct choice of electrode materials is one of the important tasks in the field of engineering electrochemical methods of purification. Changes in the main parameters (humidity, temperature, degree of acidity) in an oil-contaminated model soil, similar in composition to one of the oil fields, were investigated. Measurements of parameters when using graphite and metal electrodes were carried out at several fixed sections of the interelectrode space depending on the treatment time. The established patterns of parameter changes in the purification of oil-contaminated soils allow us to draw conclusions about the stages of the electrochemical process, its speed, and energy efficiency. The results obtained form a basis for designing industrial facilities for soil treatment.
