Impact of Sinorhizobium meliloti Exopolysaccharide on Adsorption and Aggregation in the Copper(II) Ions/Supporting Electrolyte/Kaolinite System

Abstract

To obtain insight into physicochemical interactions between Cu(II) ions, kaolinite, and exopolysaccharide (EPS) synthesized by Sinorhizobium meliloti Rm 1021 soil bacteria, an adsorption, electrokinetic, and aggregation study was performed in the selected systems. The obtained data showed that supporting electrolyte type affects both EPS and Cu(II) ions adsorption. For initial Cu(II) concentration 100 mg/L, 4.36 ± 0.25 mg/g (21.80 ± 1.00%) of the ions were adsorbed in 0.001 M NaCl and 3.76 ± 0.20 mg/g (18.80 ± 1.00%) in 0.001 M CaCl2. The experimental data were best fitted to the Langmuir model as well as pseudo second-order equation. The EPS adsorbed amount on kaolinite was higher in the CaCl2 electrolyte than in NaCl one. For an initial polymer concentration of 100 mg/L, the EPS adsorbed amount was 4.69 ± 0.08 mg/g (23.45 ± 0.40%) in 0.001 M NaCl and 5.26 ± 0.15 mg/g (26.32 ± 0.75%) in 0.001 M CaCl2. In the mixed system, regardless of electrolyte type, exopolysaccharide contributed to immobilization of higher amount of copper(II) ions on the clay mineral. Also, in the samples containing heavy metal ions and exopolysaccharide simultaneously, the aggregation of kaolinite particles was the strongest. The results presented in the paper may be very helpful in soil bioremediation, especially in the development of technologies reducing the mobility of heavy metals in the environment.

Simultaneous Removal of Pb2+ and Zn2+ Heavy Metals Using Fly Ash Na-X Zeolite and Its Carbon Na-X(C) Composite

“…The valence forces through the exchange or sharing of electrons between adsorbate and adsorbent. Such a good fitting of experimental data to PSO was also observed during the study on lead(II), chromium(VI) and copper(II) adsorption on kaolinite [ 41 , 42 , 43 ], as well as copper(II) and silver(I) ions on biochar [ 44 , 45 ]. However, it must be emphasized that some researchers do not agree with these assumptions.…”

“…Therefore, it can be assumed that Pb 2+ and Zn 2+ form monolayers on the Na-X and Na-X(C) surfaces and all adsorption sites are energetically equivalent [ 27 , 40 , 48 ]. A good fitting of experimental data to the Langmuir model was also observed for the systems: kaolinite-Pb 2+ , kaolinite-Cr(VI), kaolinite-Cu 2+ and activated biochar-Cu 2+ [ 41 , 42 , 43 , 45 ]. The obtained data also indicated that larger amounts of metal ions were adsorbed on the zeolite than on its carbon composite.…”

Carboxin and Diuron Adsorption Mechanism on Sunflower Husks Biochar and Goethite in the Single/Mixed Pesticide Solutions

“…The efficiency ( E , %) of pesticide adsorption was calculated using the equation [ 30 ]: where: C A is the concentration of pesticide adsorbed on the solid surface (mg/L); C 0 is the initial pesticide concentration in the sample (mg/L).…”

Comparison of Physicochemical Properties of Fly Ash Precursor, Na-P1(C) Zeolite–Carbon Composite and Na-P1 Zeolite—Adsorption Affinity to Divalent Pb and Zn Cations

“…[4], have been used successfully. Biochar amendments, green waste compost and triple superphosphate (TSP) as well as clay minerals, such as kaolinite [5], were applied to reduce the bioavailability of heavy metals in soils [6,7]. Another way to improve soil quality is zeolites, which have been successfully used as an additive for the composting of organic solid waste.…”