Removal of zinc ions from a soil component Na-feldspar by a rhamnolipid biosurfactant

In this study, a microbial surfactant, rhamnolipid, was investigated for its potential to enhance recovery of Zn(II) from Na-feldspar as soil component. The effects of rhamnolipid concentration, pH, and initial Zn(II) ion concentration on the removal of Zn(II) ions from Na-feldspar by rhamnolipid biosurfactant were investigated. As the concentration of Zn(II) ions in solution was increased from 0.47 to 4.08 mM, Zn(II) ions sorption to Na-feldspar decreased from 67.74 to 19.47%. As the concentration of rhamnolipid was increased from 12.5 to 100 mM, the optimum desorption efficiency of zinc ions from Na-feldspar was obtained at 25 mM rhamnolipid concentration and determined as 85.29% at 0.99 mM initial Zn(II) ion concentration in solution (1.73 mmol Zn(II)/kg Na-feldspar). To determine the effect of pH on the desorption efficiency of Zn(II) ions, pH was varied between 5.0 and 7.6. The optimum pH was obtained at 6.8 and the desorption efficency was determined as 83.87% at 0.91 mM initial Zn(II) ion concentration in solution (1.58 mmol Zn(II)/kg Na-feldspar) and 25 mM rhamnolipid concentration. As the concentration of Zn(II) loaded to Na-feldspar was increased from 1.07 to 2.49 mmol Zn(II)/kg Na-feldspar, the maximum Zn(II) desorption efficiency was 98.83% at 2.19 mmol Zn(II)/kg Na-feldspar and at 25 mM rhamnolipid concentration and pH 6.8.

The success of the bioremediation process of metal-contaminated soils by rhamnolipid biosurfactant is limited by soil texture, structure, and organic matter content. This study demonstrated that rhamnolipid washing technology can be used successfully in the bioremediation of Zn(II)contaminated soil containing Na-feldspar as a main component. The best recovery efficiency from Na-feldspar, approximately 98.83% of the sorbed Zn(II) (2.19 mmol kg−1) was achieved by adjusting the pH to 6.8 and using 25 mM rhamnolipid concentration. Na-feldspar is also a good Zn(II) sorber, this technology can also be applied to the removal of Zn(II) ions from waste waters with minor changes.