Utilization of Dielectrophoresis for the Quantification of Rare Earth Elements Adsorbed on <i>Cupriavidus necator</i>

Abstract

A new method of quantifying rare earth elements (REEs): light REEs (neodymium—Nd3+ and samarium—Sm3+) and heavy REE (europium—Eu3+) was investigated by utilizing native Cupriavidus necator as the biosorbent and dielectrophoresis as the quantification technique.C. necator was characterized as a control through the measurement of the first and second crossover frequencies in a polymer-based (PDMS) point-and-planar microwell platform at 8 Vpp (peak-to-peak voltage) ac signal and variable frequencies. Allied C. necator in its metal-bound state was then characterized for each of the REEs adsorbed. The first crossover frequency (fco1) was correlated with the amount of metal adsorbed that was obtained through spectrophotometry. The influence of pH, biosorbent dosage, initial REE concentration, and REE incubation period was further investigated to study the effects of those on the biosorption process. It was found that the amount of metal biosorbed by the C. necator is directly proportional to the biosorbent dosage and metal incubation period. Exposure to higher REE concentration solutions resulted in higher biosorption, and higher pH of REE solutions (towards neutral range) resulted in abnormal behavior due to the formation of complex salts. The results obtained here, that is, the crossover frequency versus concentration curve would serve as a baseline for other researchers, such that when the crossover frequency of a biosorbent with a particular REE is known, the quantity of that particular REE adsorbed can be correlated without the need of expensive spectrophotometric analysis.