Cu(II) Removal from Aqueous Solution by Ultrafiltration Assisted with Chestnut Shell Pigment

Polymer-enhanced ultrafiltration (PEUF) is emerging as a competent technique for removing heavy metal contaminants from effluents. Biopolymers are prospective size-enhancers due to their abundant biodegradable and renewable nature. Melanin is a type of biopolymer that binds heavy metal ions effectively. Chestnut shell pigment (CSP) is the melanin extracted from an agro-waste. This study evaluated the feasibility of employing melanin in PEUF for heavy metal removal from wastewater by using CSP and Cu(II) as the model melanin and heavy metal, respectively. The effects of pH, Cu(II), and CSP concentrations in the feed solution on the Cu(II) removal were investigated. At the optimized condition of pH 6 and a loading ratio of 33.3, more than 99% of the copper was removed by a polyethersulfone membrane with a molecular weight cut-off of 50 kDa. The binding process was rapid, completed within 22 min, and fit well with the pseudo-second-order kinetic model. The binding equilibrium data fit well with the Langmuir isotherm with a maximum binding capacity of 0.8733 mmol·g −1 . Mg 2+ and Ca 2+ hindered the Cu(II) removal, while Na + and K + affected it negligibly. Before and after Cu(II) binding, the CSP samples were characterized using Fourier transform-infrared spectrometry. The cation exchange with H + and NH 4 + ions and complexation with the carboxyl, hydroxyl, and amine groups could have been the primary mechanisms of Cu(II) binding as forms of Cu 2+ and CuOH + onto the CSP. CSP could be a promising size-enhancing biopolymer for copper removal from aqueous solutions. Graphical abstract