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The possibility of the application of spent sulfuric acid from the petrochemical industry in wet-process phosphoric acid technology was investigated. The effect of organic impurities in sulfuric acid from benzol acidic refining on the solubility of calcium sulfate hydrates is discussed. Solubility isotherms and regression equations for CaSO 4 -H 3 PO 4 -H 2 SO 4 -H 2 O (pure and containing impurities) systems are presented. Phase transition temperatures between dihydrate and hemihydrate calcium sulfate were determined. The difference between pure and polluted sulfuric acid systems observed is negligible over the range of typical wet-process phosphoric acid technology parameters. It is concluded that the application of spent sulfuric acid from benzol acidic refining does not have a negative influence on the crystallization process of dihydrate calcium sulfate and therefore can be applied in wet-process phosphoric acid technology.

This paper discusses information security of a business organization using a time-based mathematical deterministic model. The model addresses key features of a business organization from the point of view of information security and calculates the level of information security based on quantitative values. Next, the introduced model is used to evaluate the level of information security that could be achieved for known threats within a given budget. For this reason, an optimization problem of safeguard implementation is formulated and an optimization method based on dynamic programming is used to address the issue. Two samples, local and global security metrics, defined in the model are described and one of them is used in optimizing safeguard implementation.

This paper aims at demonstrating a mathematical model of the process of writing and deleting information about files on a disk, using the contents of the $MFT system file, i.e. in a file generated in the NTFS (New Technology File System). The presented model uses the language of control theory, where the state of the system is equal to the state of the disk and the state of the $MFT file, and where control is understood as undertaking the action of writing or deleting. The deterministic nature of the process and its stationarity were assumed. Then, based on the transition function after its specification, we suggest constructing further inverse images of possible prior states at subsequent stages of data writing or deletion. The obtained results form the basis for the implementations developed.