Molecular Simulations of Understanding Separation of Cadmium and Lead Ions from Aqueous Waste Water Using Directional Solvent Extraction

Abstract

In this paper, we present an all-atomistic molecular dynamics simulation study to understand the separation of cadmium (Cd 2+ ) and lead (Pb 2+ ) from the aqueous waste using directional solvent extraction (DSE) using decanoic acid (DEC) as an extractant. Different structural, dynamic, and thermodynamic properties were evaluated such as mass density profiles, radial distribution functions, self-diffusion, solvation free energy (ΔG Solv ), and transfer free energy (ΔG Transfer ). The peak intensity of mass density distribution of Cd(NO 3 ) 2 and Pb(NO 3 ) 2 shows an increase with an increase in temperature (T). The radial distribution function between the Cd 2+ and NO 3 − and Pb 2+ and NO 3 − shows a significantly higher interaction with the maximum interaction between Cd 2+ and NO 3 − . Compared to the intermolecular structure between bulk water and solvent mixed systems, we observe that metal ion water interactions are higher in bulk water, which start to decrease in the presence of a solvent. We further investigate thermodynamic analysis using free energy simulations. The ΔG Solv of Cd 2+ and Pb 2+ becomes favorable with an increase in T in DEC, while it becomes unfavorable in H 2 O. The ΔG Transfer of Cd 2+ and Pb 2+ from H 2 O to DEC becomes favorable with an increase in T. The partition coefficient (log P) values show positive values for Cd 2+ and Pb 2+ . The self-diffusion (D) of metal ions shows a 60% decrease for Cd 2+ and a 75% decrease for Pb 2+ compared to their D values in bulk water. The D values of H 2 O increase with T. Overall, we observe that the H 2 O, solvent, and metal ions are sensitive to the temperature. These molecule-level results help in guiding the solvent design for separating heavy metal ions using DSE.

Electrically Powered High-Salinity Brine Separation Using Dimethyl Ether

“…The concentration of hypersaline brines is essential for the safe disposal of industrial wastewaters and the recovery of critical metals and salts from aqueous solutions. − Many hypersaline mixtures, from salt lake and geothermal brines to mining and recycling leachates, contain minerals critical to the clean energy transition, including lithium and rare earth elements. − Brine concentration is central to minimal- (MLD) and zero-liquid discharge (ZLD) processes, minimizing the cost and environmental risk of saline waste disposal, while enabling brine valorization. Currently, concentrating highly contaminated brines often relies on evaporation ponds, which have low processing rates and a large areal footprint, imposing significant environmental costs.…”

Phytic acid modified polyacrylonitrile nanofiber membranes: Fabrication, characterization, and optimization for Pb2+ adsorption

“…5,6 The methods to remove heavy metals during wastewater treatment generally include insoluble salt precipitation, solvent extraction, ion exchange, biochemical methods, carbon/ polymer adsorption, and so forth. [7][8][9][10][11][12][13][14][15][16][17][18] The adsorption method, also called chemisorption, is a method that adsorbs heavy metals in wastewater by substantial sharing of electrons between the surface of adsorbent and metal ions to create a covalent or ionic bond, 9,10,17,19 and it is generally preferred compared to the other methods regarding its simplicity, high efficiency, cost effectiveness, and environmental friendliness. 17 Polyacrylonitrile (PAN) nanofiber membranes have been extensively applied on microfiltration, ultrafiltration, emulsified oil/water separation, and desalination, [20][21][22][23][24][25][26][27][28] due to its good weather and UV resistance, good acid resistance, high temperature resistance, and organic solvent resistance.…”