Quaternary Amine Modified Persimmon Tannin Gel: An Efficient Adsorbent for the Recovery of Precious Metals from Hydrochloric Acid Media

Abstract

Persimmon tannin was chemically modified to prepare a quaternary amine type of adsorption gel, named as quaternary amine modified persimmon tannin (QAPT) gel. The QAPT gel has been used to investigate the adsorption behaviors for Au(III), Pd(II), and Pt(IV) from HCl media. It was found that the gel exhibited good selectivity towards precious metals over a wide concentration range of HCl. However, it exhibited poor affinity towards base metals such as Cu(II), Fe(III), Ni(II), and Zn(II). The adsorption isotherms of the gel for precious metal ions were described by the Langmuir model. The maximum adsorption capacities for Au(III), Pd(II), and Pt(IV) were evaluated as 4.16, 0.84, and 0.52 mmol g⁻¹, respectively. Although the anion exchange is the main mechanism for the adsorption of anionic species of Au(III), Pt(IV), and Pd(II), adsorption of Au(III) is followed by subsequent reduction, which results in the extraordinary high adsorption capacity for Au(III). Adsorption behavior of QATP gel for Au(III) was also compared to that of the persimmon tannin, the feed material.

Keywords:

• acidic chloride media
• adsorption
• persimmon tannin
• precious metals
• quaternary amine
• reduction

ACKNOWLEDGEMENTS

The present work was financially supported by a Grant-in-Aid for Scientific Research about Establishing a Sound Material-Cycle Society (K2131) from the Ministry of Environment of the Japanese Government. The authors are also indebted to Persimmon-Kaki Technology Development. Co., Ltd., for the kind supply of the sample of crude persimmon tannin powder.

Notes

^a pH of test solution was adjusted 2.0 for adsorption of Au(III) and Pd(II).

^b pH of test solution was adjusted 1.0 for adsorption of Pt(IV).