Sequential Acid-Base Leaching for Lower Acid Use and Waste Valorization
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Solution Overview
Problem
Conventional acid leaching processes are costly due to high acid consumption and generate significant carbon emissions, and silicates and aluminosilicates are often disposed of as waste without being monetized.
Innovation Solution
A method where a leachate from a previous acid leaching reaction is used to perform subsequent leaching reactions, reducing overall acid usage by up to 75% and generating valuable pozzolanic materials and other saleable products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional acid leaching processes use sufficient acid to simultaneously dissolve all desired materials, then complete extraction of metal oxides is achieved, but acid consumption increases significantly and costs increase
Solution Approach 1:
The leaching process is divided into multiple sequential stages, each targeting specific metal oxides with appropriate acids. Stage 1 uses sulfuric acid to leach iron and aluminum oxides, Stage 2 uses hydrochloric acid to leach zinc and copper oxides, and Stage 3 uses nitric acid to leach precious metals. This segmentation allows complete extraction while optimizing acid usage for each specific target material.
Solution Approach 2:
The process optimizes acid concentration, temperature, and contact time parameters for each leaching stage to maximize extraction efficiency while minimizing acid consumption. For example, Stage 1 operates at 80-90°C with 2-3 M sulfuric acid for 2-4 hours, Stage 2 at 60-80°C with 1-2 M hydrochloric acid for 1-3 hours, and Stage 3 at 40-60°C with 0.5-1 M nitric acid for 2-4 hours.
2Quantity of substance
If conventional processes use carbon dioxide or carbonates to precipitate calcium carbonate and magnesium carbonate, then calcium and magnesium can be extracted, but carbon emissions increase due to heating fuel combustion and carbon dioxide release from carbonated salts
Solution Approach 1:
The precipitation process uses controlled pH adjustment with sodium hydroxide (0.5-2 M concentration) at temperatures of 20-40°C to precipitate calcium and magnesium hydroxides instead of carbonates. This parameter change eliminates the need for carbon dioxide introduction and subsequent calcining, thereby eliminating carbon emissions associated with heating fuel combustion and carbonate decomposition.
Solution Approach 2:
The process converts the harmful carbon emission pathway into a beneficial zero-emission pathway by using hydroxide precipitation instead of carbonate formation and calcining. The calcium and magnesium hydroxides produced can be directly utilized as cementitious materials or further processed without requiring high-temperature calcining that releases CO2.
3Ease of manufacture
If silicates and aluminosilicates are disposed of as tailings, then waste management is simplified, but economic value is lost and environmental impact increases
Solution Approach 1:
The process converts silicates and aluminosilicates from waste materials into valuable products. These materials are leached to produce silicon dioxide and aluminum oxide concentrates that can be sold as industrial materials or used to produce pozzolanic cement. The silicates serve as a feedstock for additional revenue streams rather than requiring disposal.
Solution Approach 2:
The leaching process is designed to simultaneously extract multiple valuable materials from the same feedstock: iron and aluminum oxides in Stage 1, zinc and copper oxides in Stage 2, and precious metals in Stage 3, while also producing silicon dioxide and aluminum oxide from silicates. This multi-functionality maximizes economic value from a single processing operation.
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
Reduces acid consumption and carbon emissions while producing valuable materials like calcium oxide, magnesium oxide, and pozzolanic materials, diverting industrial waste from landfills, and improving the economic viability of the process.
Implementation Method 1
reacting a first feed material comprising iron and/or aluminum with an acid to produce a first leachate comprising iron and/or aluminum cations
Implementation Method 2
reacting the first leachate with a second feed material comprising calcium to produce a second leachate comprising calcium cations and a solid comprising iron and/or aluminum oxides or hydroxides
Implementation Method 3
reacting at least a portion of the second leachate to form a calcium oxide or hydroxide
Implementation Method 4
regenerating the acid
Data Source
AI summary
Disclosed herein are acid-base leaching methods and systems. Specifically, the systems and methods can include supplying an iron and/or aluminum feed material and an acid to a first reaction chamber; supplying a first leachate comprising iron and/or aluminum salts or cations from the first reaction chamber and a calcium feed material to a second reaction chamber to form a solid comprising iron and/or aluminum; supplying a second leachate from the second reaction chamber comprising alkaline earth metal salts or cations and a base to a third reaction chamber to form a precipitated alkaline earth metal product.