Electrowinning Metallic Chromium from Acidic Waste Electrolytes
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Solution Overview
Problem
Current methods for chromium recovery from waste solutions, particularly from tanneries and electroplating plants, face challenges in achieving metallic chromium recovery while simultaneously treating sewage, with existing technologies relying heavily on costly chemical reduction and resulting in less valuable chromium compounds.
Innovation Solution
The method involves electrolysis of acidic solutions with a steel or lead anode and a cathode made of steel, graphite, or glassy carbon, using potentiostatic or galvanostatic control, or controlled pulsed current to precipitate metallic chromium directly, bypassing the expensive chemical reduction step and achieving high purity flakes, powders, or nanopowders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If chemical reduction method is used to recover chromium from waste solutions, then chromium compounds can be obtained, but the production cost increases and the product value decreases
Solution Approach 1:
The patent replaces the chemical reduction system with an electrochemical system. Instead of using chemical reducing agents to convert Cr(VI) to Cr(III) and then precipitate chromium compounds, the invention uses electrolysis with a steel anode to directly produce metallic chromium at the cathode. The steel anode dissolves to provide Cr(III) ions, which are then reduced to metallic chromium through electrochemical reduction, eliminating the need for chemical reduction agents and subsequent precipitation steps.
2Object-affected harmful factors
If chemical reduction method is used to treat chromium waste, then sewage can be treated, but the process becomes complex and requires multiple steps
Solution Approach 1:
The patent merges sewage treatment and chromium recovery into a single integrated electrolysis process. The steel anode serves dual purposes: it dissolves to provide chromium ions for recovery while simultaneously treating the chromium-containing waste solution. The electrolysis cell processes the entire waste stream in one operation, producing metallic chromium at the cathode and dissolving steel at the anode, thereby eliminating the need for separate reduction and precipitation steps.
Solution Approach 2:
The electrolysis system performs multiple functions simultaneously: it treats chromium-containing sewage, recovers valuable metallic chromium, and the steel anode continuously replenishes chromium ions in the solution. The single electrolysis cell accomplishes what would traditionally require separate chemical reduction, precipitation, and filtration systems, making the process both simpler and more versatile.
3Quantity of substance
If conventional electrolysis is used with copper or iron cathode, then chromium can be deposited, but the cathode size must be at least 10 times smaller than the anode which increases device complexity
Solution Approach 1:
The patent inverts the conventional electrolysis setup where a non-reactive cathode deposits chromium from a Cr(III) solution. Instead, the invention uses a reactive steel anode that dissolves to provide Cr(III) ions, which then migrate to the cathode for deposition. This inversion allows the anode to serve as the chromium source, eliminating the need for complex cathode size constraints and enabling more flexible electrode configurations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces costs by eliminating the chemical reduction step, producing high-purity metallic chromium (>99.7%) without the need for expensive chemical processing, making it economically viable and environmentally friendly.
Implementation Method 1
an anode made of steel or lead... wherein the electrolysis is carried out potentiostatically or galvanostatically
Implementation Method 2
a cathode made of steel, graphite or glassy carbon... to precipitate metallic chromium directly
Implementation Method 3
The method involves electrolysis of acidic solutions with a steel or lead anode and a cathode made of steel, graphite, or glassy carbon
Data Source
AI summary
The invention consists in an acidic electrolyte solution with a Cr(VI) ion concentration of more than 0.05 g/l being subjected to electrolysis using an anode made of steel or lead and a cathode made of steel, graphite or glassy carbon that is at least 10 times smaller than the anode, wherein the electrolysis is carried out potentiostatically or galvanostatically. For the lead anode, the cathode potential remains within the range from -2.9 V to -3.5 V and for the steel anode, the cathode potential remains within the range from -2.5 V to -3.0 V. The cathodic current density remains constant within the range from 0.06 A/cm2 to 0.7 A/cm2 in acidic solutions containing more than 50 g/l of chromium. Alternatively, the electrolysis is carried out using controlled current pulse, wherein the cathodic current density remains constant within the range from 0.06 A/cm2 to 0.7 A/cm2 in acidic solutions containing more than 50 g/l of chromium, and the pulse off-time is from 10 to 20% of the electrolysis duration, which is over 10 s.