Copper-containing electroplating wastewater primarily includes cyanide copper plating wastewater, acid bright copper plating wastewater, and pyrophosphate copper plating wastewater. How to recover copper from such wastewater? This article, in collaboration with a manufacturer of Online Water Quality Monitoring Instruments, explores the relevant technical principles and processes.

Pretreatment: Destruction of Copper Complexes and Oxidation of Cu⁺

Prior to copper recovery, two critical steps are required: (1) degrading copper complexes in the wastewater, and (2) oxidizing Cu⁺ ions to Cu²⁺ ions. A combined system of concentrated sodium hypochlorite and hydrogen peroxide is used to decompose cyanide and complexing agents such as potassium sodium tartrate.

Cyanide Destruction Process

Three cyanide destruction tanks are configured for sequential treatment:

1. First Cyanide Destruction Tank: Cyanide-containing and copper-containing wastewater are pumped into the tank. Lime milk is added to adjust the pH to a suitable range, with its dosage regulated by a pH control system. Simultaneously, sodium hypochlorite is introduced to initiate cyanide decomposition.
2. Second Cyanide Destruction Tank: Hydrogen peroxide is added to further degrade residual cyanide and oxidize potassium sodium tartrate. Due to the moderate reaction kinetics of this stage, a third tank is required for thorough treatment.
3. Third Cyanide Destruction Tank: The degradation efficiency of complexing agents (e.g., potassium sodium tartrate and cyanide) is verified via empirical judgment and chemical analysis. By this stage, the oxidation reaction is complete: all Cu⁺ ions are converted to Cu²⁺, and precipitates of copper hydroxide (Cu(OH)₂) and basic copper carbonate (Cu₂(OH)₂CO₃) are formed.

Copper Recovery Process

After cyanide destruction, the following steps are implemented for copper recovery:

Precipitation Enhancement: While basic copper carbonate precipitates are already formed, additional lime can convert residual Cu²⁺ into copper hydroxide precipitates.

Flocculation: The treated wastewater flows into a flocculation tank, where sodium metabisulfite is added to reduce excess hydrogen peroxide. Polyacrylamide (PAM) flocculant is also introduced to promote floc growth. Note: Without sodium metabisulfite, oxygen generated during cyanide decomposition would adsorb onto floc surfaces, causing floating. The dosage of sodium metabisulfite is controlled to just prevent floc floating.

Solid-Liquid Separation: The wastewater enters a sedimentation tank for phase separation. The sludge is transferred to a thickening tank, then dewatered via a filter press. The filter cake (enriched with copper precipitates) is collected for recovery, while the filtrate is recycled back to the wastewater adjustment tank.

Copper Content Monitoring

To quantify copper concentration in wastewater, the Hangzhou Modi T8000-Cu Total Copper Online Analyzer is recommended. This instrument adopts a colorimetry method, where copper content is calculated by measuring the absorbance change of the reaction solution (corresponding to color intensity).

This process achieves sound copper recovery efficiency while ensuring compliance with wastewater discharge standards, providing a feasible technical solution for resource recycling in the electroplating industry.