Use of spent coffee ground as a reducing agent for enhanced reduction of chromate by freezing process

Abstract

In this study, the freezing-mediated reduction of chromate (Cr(VI)) was investigated using spent coffee ground (SCG) as a reducing agent. The results obtained showed that the rate of Cr(VI) reduction using SCG was dramatically enhanced in the frozen phase (-20 °C) compared with the aqueous phase (25 °C), and after 3 h of reaction, the residual Cr(VI) concentration in the aqueous phase was 15.25 ± 0.58 ？M, while that in the frozen phase was only 1.89 ± 0.16 ？M (initial experimental conditions: [Cr(VI)]i = 20 ？M, [SCG]i = 0.1 g/L, and pHi = 3.0). Additionally, based on the results obtained under different experimental conditions, the accelerated reduction of Cr(VI) using SCG in the frozen solution could be attributed to the freeze concentration phenomenon, which is associated with the accumulation of Cr(VI) and protons, as well as the phenolic compounds in SCG extracts.