COLLOID-CHEMICAL ASPECTS OF POST-TANNING AND FILLING SOLUTION PURIFICATION

Abstract

This study investigates the purification of spent retanning and filling solutions used in the production of flexible leather, employing coagulation-flocculation reagents. Mathematical planning was used to design a multi-stage study of the complex purification process for the spent solution, and optimal quality parameters were determined. The DBSCAN method, with parameters set at epsilon 0.195 and min_point 2, was used to exclude outliers, which were considered experiments with anomalous values. As a result of mathematical modeling, 375 possible analytical dependencies of the 1st to 3rd order were obtained for each output variable based on the F-ratio from all possible combinations of process parameters. This led to the development of a mathematical model for the quality indicators of spent solution purification as a function of the consumption of the coagulant, aluminum sulfate, and the flocculants, crystalline polyhexamethyleneguanidine and its acetate. Based on the analytical dependencies of this model, the reagent consumption was optimized using the Harrington desirability function. To determine the optimal doses of coagulant and flocculants, a modified stationary Niva (Norway) coagulation test unit with six beakers (88 mm in diameter, 1 dm³ in volume) was used. Multicriteria optimization of the spent solution purification process with the Harrington desirability function established the required consumption of aluminum sulfate coagulant and the flocculants, crystalline polyhexamethyleneguanidine and its acetate. For the purification of 1 dm³ of the spent solution, the recommended doses are 0.5 g of coagulant and 0.72 g and 0.6 g of the respective flocculants.

The research indicates that the treated water (supernatant) conforms to the established standards for dry residue (MVV 081/12-0109-03), suspended solids (KND 211.1.4.039-95), and total chromium, iron, aluminum, manganese, and copper content (DSTU ISO 11885:2019).