Recovery of copper from printed circuit board (PCB) acidic etching wastewater: Ammonia regulates the crystallization of high valued copper salt

Abstract

In electronic and electrical industries, a huge amount of acidic cupric etching wastewater was produced during the manufacture of printed circuit board (PCB). Reclamation of copper is necessary for resource recovery and environmental protection. Herein, ammonia (NH3·H2O) and sodium hydroxide (NaOH) were investigated and compared as neutralizers to regulate the sequential crystallization of basic copper chloride (Cu2(OH)3Cl), copper hydroxide (Cu(OH)2), and copper sulfate (CuSO4·5H2O). Crystal phase and micro-morphology were analyzed by X-ray diffraction and scanning electron microscope; product quality was evaluated by laser particle size analyzer, thermogravimetry, and inductively coupled plasma. The results showed that ammonia as the neutralizer can regulate the formation of spherical Cu2Cl(OH)3 particles with compact surface, good fluidity, and low moisture-absorption-ability, which can be used as a precursor to producing Cu(OH)2 and CuSO4·5H2O with higher purity. Mechanism analysis revealed that ammonia acts as “a storage of OH− and Cu2+” in the aqueous phase due to its weak alkalinity and the ability to complex with Cu2+ to form stable Cu(NH3)n2+. As a result, OH− and Cu2+ were slowly released to the solution and slowed down the crystallization kinetics of copper-containing precipitates. This work proposed a promising and harmless resource recycling method, and also inspired the understanding and utilization of metal crystallization law in the ammonia buffer system.