Oral Presentation International Solvent Extraction Conference 2025

Graphical abstract

Abstract
Fisheries play a significant role in economic growth of our country that provides livelihood, ensures food security and also contributes to the export revenues. The life below water reflects ecosystem health of surface water bodies, that is necessary for attaining sustainability. However, due to increase in industrialization these ecosystems consisting of aquatic life are under threat due to getting accumulation of various toxic heavy metals such as lead, chromium, cadmium, mercury etc (1). These pollutants assemble into the fish tissues and several other aquatic animals ultimately creating a concern to human health through food chain. Therefore, development of new techniques to extract these toxic metals that are released from various industries without meeting the effluent standards into freshwater bodies is important to attain long-term sustainability.
Several conventional methods such as precipitation, adsorption, ion-exchange, electrochemical, filtration methods are being practiced in several industries in Pakistan for extraction of lead (Pb) and chromium (Cr). However, all these methods come with limitations such as high maintenance and operational costs, downstream pollution (sludge), susceptible to wastewater composition and lower extraction efficiencies. Ultrasound-assisted liquid-liquid extraction offers several advantages over conventional heavy metal extraction methods. It enhances mass transfer and metal recovery efficiency by disrupting metal-ligand bonds through acoustic cavitation. This technique requires lower solvent volumes, shorter extraction times, and operates under milder conditions, making it more energy-efficient and environmentally friendly.
Acoustic cavitation, generated using a probe sonicator, plays a critical role in enhancing the extraction of heavy metals from aqueous solutions or solid matrices. The mechanism involves the formation, growth, and violent collapse of microscopic bubbles in a liquid medium when exposed to high-frequency ultrasonic waves (typically 20–40 kHz). Due to the probe which is inserted into the sample, low-pressure voids were formed (vacuum bubbles or cavities) in the liquid, which grow, briefly oscillate and then asymmetrically implode with great intensity.
Ultrasonication-assisted extraction was performed using 1-butyl-3-methylimidazolium hexafluorophosphate with dithizone and n-hexanol as the diluent, with the collected water samples from Zebi dam and, sarki dam serving as the aqueous phase. The organic and aqueous phases were mixed in a 1:1 (v/v) ratio in a conical flask and subjected to sonication. Post-sonication the mixture was centrifuged at 3500rpm for about 10-15min, and the samples were evaluated for Pb and Cr trace metals using ICP-MS. Design of experiment, statistical analysis and optimization was carried out using response surface methodology (RSM). Design of experiment was carried out to understand the impact of the influential parameters, pH- 2-7, extractant to diluent ratio – 5-20% and extraction time – 5min-60min as independent variables and the overall extraction efficiency as the response (2).
Results of the study showed that both the metals were successfully extracted at optimized experimental conditions. The overall extraction removal efficiency for Pb and Cr were above 90% and in between 90-95% respectively. Extraction efficiency was evaluated to be higher at lower pH conditions between pH values of 2-4, the pH of the sample ensured the stability of the metals present in the solution. However, the extractant-to-diluent ratio – 5-20% affected the extraction capacity, with higher ratios improving efficiency, but excessive ratios may hinder phase separation due to third phase formation. Extraction time – 5–60 minutes demonstrated that longer durations generally enhanced extraction efficiency, although prolonged times beyond equilibrium resulted in excessive energy utilization. Therefore, the optimizing of these parameters is crucial for maximizing heavy metal extraction efficiency.
References
1. Saeed S, Waheed N, Ahmad Z, Saleem R, Naseer A, Afridi N, et al. Unveiling the Impact of Heavy Metal Lead on Hypophthalmichthys molitrix : Insights into Behavioral and Haematological Alterations. 2024;
2. Kończyk J. Selective solvent extraction of some heavy metal ions from aqueous solutions by octafunctionalized resorcin[4]arenes. Physicochem Probl Miner Process. 2020;56(2):271–85.