Comparison between sinusoidal AC coagulation and conventional DC coagulation in removing Cu2+ from printed circuit board wastewater

Abstract

A new Electrocoagulation (EC) technique, sinusoidal AC coagulation (SACC), is creatively put forward for Cu²⁺ removal in the wastewater from the printed circuit board (PCB) production in this paper. The removal efficiency of Cu²⁺ from PCB wastewater and energy consumption are compared by SACC and conventional direct current coagulation (DCC). The optimal process parameters were established through analysis of response surface methodology (RSM). The coagulations containing Cu²⁺ was characterized by SEM, EDS, TEM，BET, XRD and FTIR. The nano-ferrum collosol, mainly composed of goethite (α-FeOOH) and magnetite (γ-Fe₂O₃), absorbs the Cu²⁺ and coagulates to remove Cu²⁺. The results show that the removal rates of Cu²⁺ by SACC and DCC are 99.86％ and 98.21％, respectively, and the energy consumption is 2.76 × 10^-2 kWh⋅m^-3 for SACC and 4.42 × 10^-2 kWh⋅m^-3 for DCC under the optimal process conditions of c₀ (Cu²⁺) = 41.99 mg⋅dm^-3, pH = 7.14, j = 0.293 A⋅m^-2, t = 16.7 min. The pilot tests indicate that the SACC technique is feasible in industrial application. Cu²⁺ removal were completed through electrodeposition of Cu²⁺ on iron electrode, the deposition of Cu(OH)₂ and the adsorption of Cu²⁺ by ferrum collosol. The adsorption follows the pseudo-second order kinetics model well. The maximum saturated adsorption capacity (q_max) of Cu²⁺ on ferrum collosol produced by SACC is larger than that by DCC. The adsorption of Cu²⁺ on the ferrum collosol prepared by SACC and DCC are in accordance with Langmuir's adsorption isotherms. The novel SACC technique is a promising technique for the highly-efficient treatment of Cu²⁺ from PCB wastewater.

Keywords: Cu(2+) removal; Electrocoagulation; Response surface methodology; Sinusoidal alternating current; Wastewater.