Reduction of Fluoride in Central Kyzylkum Phosphate Waste in an Acidic Environment: Experimental and Mathematical Study Based on the Langmuir Model
Abstract
Below is a scientific article explaining the results of a comprehensive study on the desorption of fluoride from mineralized waste (MM) of the Central Kyzylkum phosphate deposits in an acidic environment, studied by experiments and mathematical modeling. The interaction between fluorapatite present in MM and acidic wastewater (AWW) was studied in detail. Acidic components in AWW, mainly free fatty acids, promote the decomposition of fluoride in MM through ion exchange mechanisms. Experiments were performed at 333 K with 30 minutes of mixing for different AWW: MM mass ratios from 100:10 to 100:40. The initial pH of the MM samples was close to neutral, while the pH of the AWW was 2.2; therefore, the pH in the mixtures was acidic. Values of qₑ (fluoride adsorbed per unit mass) and Cₑ (equilibrium fluoride concentration) were calculated for each mixture. Using these data, a regression graph was plotted according to the Langmuir adsorption model. A linear equation obtained from the graph gave qmax = 7.48 mg/g and KL = 0.027 L/mg. An R² value of 0.93484 obtained from the Langmuir equation showed that the model and experimental results are in good correlation. Fluoride ions in AWW can be converted into HF gas by strong acids and released into the atmosphere. The identification of reaction products allowed them to propose a mechanism of decomposition. Two different streams of industrial wastes, MM and AWW, were combined in the current work, and this combination allowed the development of new technological solutions.