Questions and Answers
What is solid-liquid extraction?
The process of separation of soluble constituents of a solid material using a suitable solvent.
Which of the following are steps in solid-liquid extraction? (Select all that apply)
What is leaching?
The preferential solution of one or more constituents of a solid mixture by contact with a liquid solvent.
What is the main purpose of crushing and grinding solids for leaching?
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Leaching can be used to recover sugar from sugar beets.
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Leaching is commonly used in the extraction of minerals from ores, such as copper from its ores using ___ solutions.
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What is decoction in the context of solid-liquid extraction?
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Which of the following processes refers to washing soluble materials off a solid surface?
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What is leaching?
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Which of the following are types of leaching agents? (Select all that apply)
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What is the primary application of leaching in metallurgical processes?
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Smaller particle sizes increase the leaching rate.
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What environmental issue is caused by leaching?
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What is acid mine drainage?
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Which of the following affects leaching kinetics? (Select all that apply)
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What is the concept of practical equilibrium in leaching?
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What is the purpose of shank tanks in the leaching process?
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Agitated leach tanks are designed for ______ mixing and enhanced contact.
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Study Notes
Solid-Liquid Extraction
- Solid-liquid extraction separates soluble components of a solid using a suitable solvent.
- Involves four key steps:
- Contact between solid feed and solvent
- Separation of the extracted solution from the solid
- Solvent removal from the extract, followed by product purification
- Solvent recovery from the remaining moisture in the solid
Classification of Solid-Liquid Extraction Systems
- Diffusional extraction: mass transfer resistance primarily exists in the solid phase.
- Washing extraction: occurs with small solid particle sizes, making solid-phase diffusion resistance minimal; extraction resembles a washing process.
- Leaching: involves dissolving one or more substances from solid particles via chemical reactions, often using acids, alkalis, or complexing agents.
Introduction to Leaching
- Leaching enables preferential dissolution of one or more constituents from a solid mixture using a liquid solvent.
- Historically relates to percolation of liquid through solid beds, referred to as extraction or decoction when using boiling solvents.
- Elutriation or elution refers to washing off surface-soluble materials.
Applications in Metallurgy and Natural Products
- Metallurgical industries are the largest users of leaching for separating valuable minerals from undesirable constituents.
- Processes include:
- Copper minerals dissolved using sulfuric acid or ammoniacal solutions.
- Gold separation using sodium cyanide solutions.
- Leaching applied in processing aluminum, cobalt, manganese, nickel, and zinc.
- Naturally occurring products separated by leaching include:
- Sugar extracted from sugar beets using hot water.
- Vegetable oils obtained from soybeans and cottonseed with organic solvents.
- Tannins extracted from tree barks using water.
- Pharmaceutical products sourced from plant roots and leaves.
- Tea and coffee prepared through leaching.
Preparation of the Solid
- Crushing and grinding of solids enhance leaching effectiveness, opening up the soluble material for solvent access.
- Example: A specific copper ore leached more efficiently when ground to pass through a 60-mesh screen within 4 to 8 hours versus 5 days for 6-mm granules and 4 to 6 years for 150-mm lumps.
- Size reduction is crucial; a 100-mesh grind is necessary for certain gold ores embedded in quartzite.
- In plant and animal tissues, natural products reside within cellular structures; intact cell walls slow down solute dissolution.
- Sugar beets are sliced into wedges (cossettes) before leaching to expedite solvent access to cell interiors.
Theoretical Principles Of Leaching
- Leaching extracts soluble components from solids using liquid solvents.
- Involves solute diffusion from solid to liquid, described by Fick's laws.
- Equilibrium is reached when solute concentration in liquid remains constant.
Leaching Agents
- Acids: Sulfuric acid is a common choice for metal extraction.
- Bases: Sodium hydroxide is utilized for certain mineral extractions.
- Complexing Agents: EDTA forms stable complexes with metal ions.
- Selection of leaching agents depends on solubility, reactivity, and environmental impact.
Applications In Resource Recovery
- Metallurgical Uses: Extract metals like copper and gold from ores.
- Agricultural Uses: Recover nutrients from organic waste via compost leachate.
- Environmental Uses: Remediate soils and water contaminated with pollutants.
Leaching Kinetics
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Factors influencing kinetics:
- Smaller particle size increases surface area and leaching rate.
- Elevated temperature typically enhances solubility and diffusion.
- Stirring and agitation improve mixing and mass transfer.
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Kinetic Models:
- First-order kinetics shows a linear relationship with solute concentration.
- Diffusion-controlled models indicate rate limitation due to solute diffusion.
Environmental Impacts Of Leaching
- Leachates may introduce contaminants into groundwater, leading to pollution.
- Heavy metals in leachates pose a risk of toxic element mobilization.
- Acid mine drainage results from sulfide mineral leaching, producing acidic water.
Practical Equilibrium
- Practical equilibrium reflects a balanced extraction process with no net solute concentration change.
- Influenced by solute concentrations in solid and liquid phases, along with temperature and pressure conditions.
Shank Tanks
- Shank tanks facilitate effective contact during the leaching process.
- Designed for either continuous or batch operation with mixing capabilities to enhance mass transfer.
- Widely used in the mineral processing industry for efficient leaching.
Leaching Equipment
- Agitated Leach Tanks: Provide uniform mixing and improved contact between phases.
- Percolation Columns: Enable gravity-assisted leaching processes.
- Heap Leaching Systems: Applied to low-grade ores; leaching agents are distributed over ore heaps.
- Considerations include compatibility of materials with leaching agents and the scale of operation (laboratory, pilot, industrial).
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Description
Explore the principles and classifications of solid-liquid extraction in this quiz. Understand the key steps involved in the process, including contact with solvents, separation, and recovery techniques. Delve into various extraction systems such as diffusional, washing extraction, and leaching for comprehensive knowledge.
