Metal Hydroxide Precipitation via Lime Cream Thickening
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Solution Overview
Problem
Existing methods for treating metal-containing solutions, such as those with nickel, cobalt, zinc, or copper, face challenges in efficiency and cost-effectiveness, particularly due to the use of expensive precipitants like sodium hydroxide and the need for additional flocculants, which increase operational costs and complexity.
Innovation Solution
A method involving the use of lime cream as a precipitant to treat metal sulfate solutions, generating calcium sulfate and metal hydroxide precipitates with different settling velocities, allowing for their separation without additional flocculants, thereby reducing production costs and improving yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If expensive precipitants like sodium hydroxide are used to treat metal-containing solutions, then the metal hydroxide precipitate can be obtained, but the production cost increases significantly
Solution Approach 1:
The patent replaces expensive precipitants like sodium hydroxide with cheap lime cream (calcium hydroxide suspension). Although lime cream produces calcium sulfate precipitate that needs separation, the overall cost is dramatically reduced. The lime cream serves as a disposable, low-cost reagent that achieves the primary goal of metal hydroxide precipitation without the high material costs of conventional precipitants.
Solution Approach 2:
The patent changes the chemical parameter of the precipitant from strong base (sodium hydroxide) to weak base (calcium hydroxide), and controls the pH range at 9.5-10.5 to optimize both precipitation efficiency and calcium sulfate formation. This parameter change enables the use of cheaper reagents while maintaining effective metal hydroxide precipitation.
2Productivity
If additional flocculants are added to improve precipitate settling, then the separation efficiency increases, but the operational cost and process complexity increase
Solution Approach 1:
The patent exploits the self-settling property of calcium sulfate precipitate, which naturally forms dense, easily separable crystals without requiring additional flocculants. The calcium sulfate acts as a self-sufficient precipitate that facilitates its own separation from the liquid phase through gravity settling, eliminating the need for external chemical additives and complex separation equipment.
Solution Approach 2:
The patent converts the potential harm of having two precipitates (calcium sulfate and metal hydroxide) into a benefit by utilizing the different settling characteristics of each. The calcium sulfate precipitate, which might be considered an impurity, actually aids in the separation process by forming a distinct, easily settleable phase that can be removed first, simplifying the overall separation sequence.
3Quantity of substance
If lime cream is used as precipitant to reduce cost, then both calcium sulfate and metal hydroxide precipitates are generated, but the separation process becomes more challenging
Solution Approach 1:
The patent segments the separation process into two distinct stages: first separating calcium sulfate through gravity settling in a thickener, then filtering the metal hydroxide from the remaining liquid. This segmentation exploits the different physical properties of the two precipitates, making the separation manageable despite the complexity of dealing with dual precipitates.
Solution Approach 2:
The patent uses a thickening tank as an intermediary device between precipitation and final filtration. This intermediate step allows calcium sulfate to settle and be partially removed before the metal hydroxide filtration, acting as a mediator that simplifies the overall separation task by handling one precipitate type first.
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 method achieves a direct yield of 96% for metals like nickel, cobalt, and zinc, with costs saved by over 2,000 Yuan per ton compared to existing technologies, and is suitable for large-scale industrial application.
Implementation Method 1
the metal sulfate in the metal-containing solution reacts with the calcium hydroxide in the lime cream to generate calcium sulfate and metal hydroxide
Implementation Method 2
the calcium sulfate exists in the form of crystals, while the metal hydroxide exists in a flocculation state, such that a settling velocity of the calcium sulfate is greater than that of the metal hydroxide
Data Source
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AI summary
The present disclosure provides a method for treating a metal-containing solution, in which the metal is selected from nickel, cobalt, zinc or copper, and the metal-containing solution comprises a metal sulfate. The method includes: (1) mixing the metal-containing solution with lime cream to obtain a liquid-solid mixture; (2) performing a thickening treatment on the liquid-solid mixture to obtain an overflow containing a metal hydroxide precipitate and an underflow containing calcium sulfate; and (3) filtering the overflow containing the metal hydroxide precipitate to obtain the metal hydroxide and a filtrate.