Choke Nozzle Cavitation for Gold Leaching Gas Hold-Up
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Solution Overview
Problem
Existing methods for injecting oxygen into slurry or pulp for gold extraction and other chemical processes face challenges with low gas hold-up and utilization efficiencies due to large bubble formation and resistance to mixing, leading to incomplete oxidation and high cyanide consumption.
Innovation Solution
A fluid treatment apparatus utilizing choke nozzles with converging and diverging sections to create choked flow conditions, generating ultra-fine bubbles through cavitation, which enhances gas diffusion and chemical reactions by implosion of bubbles into nanometre or picometre sizes, improving gas hold-up and reaction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional lance/nozzle injection with agitator mixing is used, then gas injection capability is provided, but large bubbles are created resulting in low gas hold-up and low utilization efficiency
Solution Approach 1:
The invention segments the gas injection process into multiple stages: initial gas injection through the choke nozzle, followed by intensive mixing in the reaction chamber with high-speed impellers. This segmentation allows gas to be broken into smaller bubbles through controlled mixing rather than creating large bubbles in a single step, thereby increasing gas hold-up and utilization efficiency
Solution Approach 2:
The invention employs dynamic mixing elements including high-speed impellers that rotate at controlled speeds to create turbulent flow patterns. This dynamic mixing approach continuously breaks up gas bubbles and redistributes them throughout the slurry, preventing bubble coalescence and maintaining high gas hold-up levels while improving mass transfer efficiency
2Ease of operation
If gas injection through pipes, slots, or porous media relying on turbulence is used, then gas dispersion is improved, but relative gas hold-up and utilization efficiencies remain relatively low
Solution Approach 1:
The invention utilizes a choke nozzle designed to create a jet flow pattern when gas is injected under pressure. The nozzle geometry converts pressure energy into kinetic energy, creating a high-velocity gas jet that penetrates the slurry and creates fine bubble dispersion. This pneumatic approach, combined with hydraulic mixing in the reaction chamber, achieves superior gas hold-up compared to passive turbulence-based methods
3Ease of operation
If venturis or eductors creating suction are used, then gas is drawn into slurry, but larger bubbles are created which can flash off and gas hold-up remains relatively low
Solution Approach 1:
The invention converts the potential harm of bubble flashing (which occurs when pressure drops too low) into a benefit by using controlled pressure gradients. The choke nozzle maintains sufficient backpressure to prevent excessive bubble expansion, while the subsequent mixing zone creates conditions for controlled bubble breakup. This approach prevents bubble flash-off while still achieving effective gas dispersion and high gas hold-up
4Ease of operation
If high shear mixing is used to disperse gas, then gas mixing is achieved, but Reynolds Numbers are relatively low resulting in large bubbles and low dissolved gas levels
Solution Approach 1:
The invention performs preliminary gas injection and bubble formation in a dedicated injection zone before the main mixing chamber. The choke nozzle pre-conditiones the gas by creating fine bubbles under controlled pressure, and then the high-speed impellers in the reaction chamber intensively mix the pre-dispersed gas with the slurry. This preliminary action prevents the need for excessively high Reynolds Numbers while achieving high dissolved gas levels
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 apparatus significantly increases gas hold-up and mass transfer in fluids, accelerating chemical reactions, reducing cyanide consumption, and improving gold recovery and metal leaching efficiency, while also facilitating arsenic remediation and cyanide destruction.
Implementation Method 1
enhancing chemical or physical reactions occurring in processes by utilizing choked flow
Implementation Method 2
may provide associated hydraulic cavitation
Implementation Method 3
generating ultra-fine bubbles through cavitation, which enhances gas diffusion
Implementation Method 4
choke nozzles with converging and diverging sections to create choked flow conditions
Implementation Method 5
significantly increases gas hold-up and mass transfer in fluids, accelerating chemical reactions
Data Source
AI summary
Liquid treatment apparatus comprises at least two chambers being first and second chambers through which a fluid can flow. The two chambers are separated by at least one choke nozzle which has an entrance in the first chamber and an exit in the second chamber. The choke nozzle comprises a converging section at its entrance, a throat section, a backward-facing step immediately after the throat section, and an exit section at its exit wherein the exit section diverges from the step. Similarly constructed mixing nozzles may be included in the apparatus. The apparatus is especially useful in processes requiring a gas to be entrained in a fluid so that the gas is in the form of very small bubbles that do not tend to coalesce and flash off such as in the dissolution of gold and other precious metals from ore and in the removal of arsenic from an ore.