Ultrasound-improved removal of chloride ions from coking circulating water by Friedel’s salt precipitation: Efficiency enhancement and mechanisms

Abstract

The concentration of chloride ions should keep appropriate in the coking circulating water to prevent multiple detrimental effects on the environment. Even though Friedel’s salt precipitation is a practical and economically beneficial method to remove chloride, the chloride removal of traditional method is insufficient. A modified ultrasonic method for the removal of chloride by Friedel’s salt precipitation was proposed. A number of influential elements including the ratio of reagents, reaction time, pH, temperature, stirring speed, sulfate, and fluoride, were fully investigated. The results showed that sulfate and fluoride could inhibit the chloride removal through a competitive effect with chloride. With ultrasonic enhancement, the optimal removal efficiency of chloride ions was 87.20 %, compared to 82.17 % without ultrasonic enhancement. Additionally, the reaction time was shortened by 15 minutes utilizing ultrasonic. The cavitation and mechanical disruption effects of ultrasound conjunction with precipitation can improve the efficiency of chloride removal. This study provided a theoretical foundation of ultrasonic synergistic Friedel’s salt precipitation method for chloride removal, and offered guidance for the use of Friedel’s salt with enhanced techniques in other fields.