Evaluation of Nickel Removal Efficiency from Wastewater by Electrochemical Method Using Graphite–Stainless Steel Electrodes

This study evaluated the efficiency of nickel ion (Ni2+) removal from electroplating wastewater using a laboratory-scale electrochemical system equipped with a non-sacrificial graphite anode and a grade 304 stainless steel cathode. The primary objective was to investigate the influence of key operational parameters, including initial solution pH (7.0-9.0), applied voltage (5.0-15.0 V), electrolysis duration (30.0-120.0 min), and initial nickel concentration (C0 = 567.00 mg/L) to identify optimal processing conditions, determine specific energy consumption, and evaluate complete nickel mass balances across system phases. Residual nickel concentrations were quantitatively analyzed using Flame Atomic Absorption Spectrometry (F-AAS) according to SMEWW 3111B:2023, while system stability was evaluated by monitoring total dissolved solids (TDS) and electrical conductivity (EC) across triplicate runs (n = 3). Experimental results demonstrated that under optimal operational parameters (pH 7.0, applied voltage 10.0 V, and electrolysis duration 60.0 min), the maximum nickel removal efficiency reached 78.94%, reducing the residual concentration to 119.41 mg/L with a low specific energy consumption of 0.285 kWh/m3. A neutral medium (pH 7.0) exhibited superior operational stability (SD = 2.62, RSD = 3.83 %). Applied voltage proved to be a critical determinant for cathodic metal deposition; however, raising the potential to 15.0 V triggered parasitic hydrogen evolution, substantially increasing energy consumption to 0.612 kWh/m3 with marginal efficiency gains. Comprehensive mass balance calculations confirmed that 91.2% of the removed nickel was recovered directly as solid elemental plating on the cathode, while 8.8% formed loose hydroxide precipitates. Although direct electrolysis avoids primary chemical sludge generation, the remaining residual nickel concentration (119.41 mg/L) exceeds national discharge thresholds (QCVN 40:2025/BTNMT, Column A), highlighting the necessity of combining this process with downstream polishing stages (e.g., ion exchange or nanofiltration). Overall, the graphite–stainless steel system offers a sustainable, low sludge alternative for direct heavy metal recovery in industrial wastewater management.

Electrochemistry, electroplating wastewater, graphite–stainless steel electrode, mass balance, nickel removal.

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