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The IX International Congress “Engineering, Environment and Materials in Process Industry”—EEM2025 took place in Ethno Village Stanišići, Bijeljina, Republic of Srpska, Bosnia and Herzegovina, from 2 to 4 April 2025

In this paper, the influence of steel type, inhibitor concentration, and time on the inhibitory effect of dandelion root extract in a 4% HCl solution was investigated. Two types of steel of known composition were used, and the inhibitory effect was monitored in a time interval of 2, 4, 6, 24, and 48 h. Dandelion root extract was obtained by the Soxhlet method with 96% ethanol, and then dilutions (0.5 g/L, 1.0 g/L, and 1.5 g/L) were made from the obtained extract in a 4% HCl solution. The optimization of the experimentally obtained results was performed using MINITAB 21 software. The optimal concentration of dandelion roots in the 4% HCl solution in terms of the inhibitory effect is 1.5 g/L, while time has no great influence on the inhibitory effect because the beneficial effect was already achieved after 2 h. In addition, better inhibition efficiency was observed in steel type 1.