Zinc Waste Treatment via Segmented Neutralization and Grading
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Solution Overview
Problem
Current methods for treating zinc-containing waste liquids in zinc hydrometallurgy processes are inefficient, resulting in hazardous neutralized slag and high recovery costs, with limited metal recovery and poor purity of gypsum products due to premature precipitation of metal ions at acidic pH levels.
Innovation Solution
A system and method involving a neutralization device, grading device, and sedimentation-filtration unit that separates zinc hydroxide and calcium sulfate by particle size, utilizing a rotary water inlet to create a vortex flow for efficient grading and subsequent zinc recovery through flocculation and filtration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lime neutralization is used to treat zinc-containing waste liquid, then the waste liquid can be neutralized and metal ions precipitated, but a large amount of hazardous neutralized slag is generated and zinc cannot be reused
Solution Approach 1:
The treatment process is divided into two distinct stages: first stage for gypsum precipitation at low pH (1.5-3.0), and second stage for metal ion precipitation at high pH (9.0-11.0). This segmentation allows selective recovery of zinc as gypsum in the first stage, preventing zinc loss in the final slag and enabling zinc reuse.
Solution Approach 2:
Gypsum precipitation is performed as a preliminary action before metal ion precipitation. By adjusting pH to 1.5-3.0 first, zinc sulfate reacts with calcium carbonate to form gypsum precipitate, which is then separated. This preliminary gypsum removal prevents zinc from being incorporated into the hazardous slag in the subsequent high-pH neutralization step.
2Quantity of substance
If two-stage method is used to treat waste acid with pH control, then gypsum can be obtained at first stage, but metal ions are still precipitated at relatively low pH causing limited gypsum purity
Solution Approach 1:
Different pH conditions are applied locally to different stages: the first stage maintains pH 1.5-3.0 specifically optimized for gypsum precipitation, while the second stage uses pH 9.0-11.0 for metal ion precipitation. This local quality control ensures high purity gypsum is formed in the first stage before any metal ion contamination occurs.
Solution Approach 2:
The pH parameter is changed in a controlled sequence: first adjusted to 1.5-3.0 for gypsum precipitation, then increased to 9.0-11.0 for metal ion precipitation. This parameter change strategy prevents metal ions from precipitating during gypsum formation, ensuring gypsum purity while maintaining high production quantity.
3Object-affected harmful factors
If existing treatment methods are used to meet wastewater discharge standards, then discharge requirements can be satisfied, but valuable metals are not recovered or recovery cost is high
Solution Approach 1:
The harmful acidic waste liquid containing zinc is converted into a beneficial resource through the two-stage process. In the first stage, zinc sulfate is transformed into gypsum precipitate, which is a valuable byproduct. This converts the harmful waste stream into a source of recoverable materials, simultaneously achieving discharge compliance and metal recovery at low cost.
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
Enables efficient gradation and recovery of zinc and calcium sulfate with different particle sizes, simplifying the process for industrialization and reducing costs by achieving high purity zinc-rich slag and calcium sulfate recovery.
Implementation Method 1
water enters the bottom column along a tangent line of an inner sidewall of the bottom column and forms a vortex flow upward
Implementation Method 2
The solid calcium sulfate particles with a larger specific gravity or particle size in the mixed slurry are settled downwards
Implementation Method 3
the mixed slurry containing zinc hydroxide and calcium sulfate can be obtained, which is fed to the upper column
Implementation Method 4
after the acidic zinc-containing waste liquid reacts with the neutralizer
Data Source
Figure 1~2
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Figure 5~7
AI summary
A system for treating a zinc-containing waste liquid includes: a neutralization device, having a zinc-containing waste liquid inlet, a neutralizer inlet and a mixed slurry outlet; a grading device, including from top to bottom: an upper column, a bottom column, and a transition column connecting the upper column and the bottom column; and a sedimentation-filtration unit, having a zinc hydroxide slurry inlet, a flocculant inlet, a zinc-rich slag outlet and a filtered liquid outlet. The upper column has an open top, and includes a mixed slurry feeding pipe connected to the mixed slurry outlet, an overflow trough disposed at an outer sidewall of an upper part of the upper column, and a zinc hydroxide slurry outlet disposed at a bottom of the overflow trough. The bottom column includes a rotary water inlet pipe and a calcium sulfate slurry outlet disposed above the rotary water inlet pipe.