Optimal evaporation regime of alkaline solution obtained from cotton stalk ash and chemical analysis of precipitation process

Abstract

This article describes a comprehensive analysis of the optimal evaporation method for an alkaline solution that is prepared using the aqueous extract of cotton stalk ash, along with the investigation of the chemical composition of the precipitation that appears during evaporation of the solution. Cotton stalk ash is regarded as a secondary product from burning biomass in household appliances, specifically in tandir ovens used to bake bread and somsa, and is currently being discarded into the environment. In the presented research, the procedure for preparation of the alkaline solution was conducted under optimal conditions, when the mixture of ash and water with the weight ratio of 1:5 was boiled. Then, filtration and evaporation of the obtained suspension were performed. From the results obtained, the optimal evaporation regime was identified as 75%, as during this regime no precipitation occurs. Nevertheless, at a level of evaporation of 80%, the precipitation phenomenon was discovered in the solution due to the disturbance of solubility equilibrium. The content of the precipitated components in relation to cations was estimated using flame photometry, and the phase composition was evaluated with FTIR spectroscopy. Thus, it was found that the precipitate mainly contains carbonate-like compounds. It was proved that potassium ions prevailed in the solution, and their molar concentration is much greater than that of other cations. Moreover, when the concentration is high, a certain share of potassium ions is transferred from the solution into the precipitate phase. As calculated, the total alkalinity of the prepared solution equals 3.41 N and constitutes about half of the alkalinity of the 6 N NaOH solution employed in the vegetable oils purification process.