Lime-Treated Tailings Dewatering for Sustained Shear Strength
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Solution Overview
Problem
Existing tailings treatment methods, such as using gypsum, alum, or calcium chloride, fail to provide sufficient and permanent increase in undrained shear strength, making it difficult to meet regulatory standards for reclamation and landform development due to low or temporary strength development.
Innovation Solution
Treatment of tailings with calcium hydroxide to achieve a pH of at least 11.5 and controlled soluble calcium levels, followed by a flocculant and additional calcium hydroxide to promote pozzolanic reactions, forming calcium silicate and aluminate hydrates for a cementitious crust with sustained shear strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional coagulants (gypsum, alum, calcium chloride) are used to treat tailings, then dewatering can be achieved, but the undrained shear strength remains low or temporary, failing to meet regulatory reclamation standards
Solution Approach 1:
The patent changes the chemical parameters of the treatment process by using calcium hydroxide to achieve high pH levels (≥11.5) and controlled soluble calcium levels, which promotes pozzolanic reactions. This chemical parameter change transforms the tailings matrix to develop sustained undrained shear strength, resolving the contradiction between achieving dewatering and obtaining permanent strength improvement.
Solution Approach 2:
The patent creates a composite material system through the formation of calcium silicate and aluminate hydrates via pozzolanic reactions. This composite cementitious crust forms within the tailings matrix, providing permanent structural strength and stability, thereby resolving the issue of temporary or insufficient strength development with conventional coagulants.
2Strength
If high pH and soluble calcium levels are maintained to promote pozzolanic reactions, then sustained shear strength is achieved, but the process complexity and chemical control requirements increase
Solution Approach 1:
The patent employs self-service principles by utilizing the tailings material itself as the source of reactive silica and alumina components. The high pH environment promotes pozzolanic reactions between the added calcium hydroxide and the inherent clay minerals in the tailings, creating a self-sustaining chemical process that develops strength without requiring complex external chemical additives or sophisticated control systems.
Solution Approach 2:
The patent simplifies process control by focusing on achieving and maintaining two key parameters: pH ≥11.5 and controlled soluble calcium levels. By targeting these specific parameter ranges, the complex chemical process becomes more manageable, allowing sustained strength development through pozzolanic reactions while reducing the need for multiple chemical additives and complex process monitoring.
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
The method results in tailings with increased and sustained undrained shear strength, allowing for effective reclamation and meeting regulatory requirements, with a solids content of at least 40% by weight.
Implementation Method 1
achieve a pH of at least 11.5 and controlled soluble calcium levels, followed by a flocculant and additional calcium hydroxide to promote pozzolanic reactions, forming calcium silicate and aluminate hydrates for a cementitious crust with sustained shear strength
Implementation Method 2
combining the first mixture with a flocculant to form a second mixture, wherein the flocculant is configured to bond with clay of the first mixture while releasing process water
Implementation Method 3
The pH and soluble calcium level promote pozzolanic reactions to occur within the mixture
Data Source
AI summary
Methods and systems for treating tailings at an elevated pH using lime are disclosed herein. In some embodiments, the method comprises (i) providing a tailings stream comprising bicarbonates and a pH less than 9.0, (ii) adding a coagulant comprising calcium hydroxide to the tailings stream to form a mixture having a pH of at least 11.5 and a soluble calcium level no more than 800 mg/L, and (iii) dewatering the mixture to produce a product having a solids content of at least 40% by weight. In some embodiments, the pH and soluble calcium level of the mixture cause chemical modification of clay materials of the mixture via pozzolanic reactions. In some embodiments, the undrained shear strength of the product increases over a period of time of at least two days.