MASS TRANSFER - 2

TERM PROJECT
COMMON SALT PRODUCTION

Presented by: Harsh Sharma,

Lokesh Kumar,
Presented to : PK VIJAYAN Kailash Meghwal
Title & Introduction: The Essential Compound (NaCl)

Chemical Composition: Common salt is Sodium Chloride (NaCl), composed

of ≈40% sodium and 60% chloride.

Physiological Importance :
Conducting nerve impulses.
Contracting and relaxing muscles.
Maintaining proper water and mineral balance in the body.

Culinary & Preservation Roles :

Flavor enhancer, binder, and stabilizer.
Crucial food preservative (bacteria cannot thrive in high salt concentration due to osmotic pressure).
 Chemical and Physical Properties of Sodium Chloride
Structure: Forms colorless crystals with a Face-Centered Cubic (FCC) lattice structure.

Thermal Stability: High melting and boiling points, critical for high-temperature
refining.
Solubility: High solubility permits the formation of saturated brine necessary for
solution mining and crystallization yield.
Key Physico-Chemical Properties of NaCl
Property Value Relevance to Industrial Processing

Compound Formula NaCl Feedstock identification.

Molecular Weight 58.44 g/mol Stoichiometric calculations.

Melting Point 801°C (1,474∘ F) Thermal stability for evaporative systems.

Density 2.16 g/cm3 Affects centrifugal separation and handling.

Solubility in H2​O (273K) 35.7 g/100 mL Defines saturation limits and crystallization
yield.
Crystal Structure Face-Centered Cubic (FCC) Influences mechanical properties.
 Analysis of Primary Production Methods

Primary Mass Transfer

Production Method Source Material Typical Purity Profile Controlling Constraint
Technique

Sea water or salt lake Lower to Medium Climate (Evaporation

Solar Evaporation Natural Evaporation
brine Purity > Precipitation rate)

Geological
Subterranean Halite Physical
Rock Mining Medium Purity availability, physical
Deposits Extraction/Crushing
access
Forced Energy input, brine
Evaporated (Solution Underground
Evaporation/Vacuum High Purity (99.6%+) purification
Mining) manufactured brine
Crystallization complexity
 Mass Transfer in Salt Production: Evaporation and
Crystallization
Core Principle: Controlled mass transfer (movement of solvent/solute) is
key to salt recovery.
Two Types of Mass Transfer:
Evaporation (Liquid-Vapor Transfer): Water moves from liquid brine to gaseous steam (natural or
forced/thermal).
Crystallization (Liquid-Solid Transfer): Solute (NaCl) transfers from supersaturated liquid to solid
crystal.

Forced Mass Transfer Technologies:

Modern production uses Vacuum Crystallizers operating under low pressure.
Benefits: Lowers boiling point, enabling energy-efficient crystallization; prevents thermal degradation
ensures superior quality and high yield by controlling crystal growth.
Rock Salt Mining Techniques
Extraction Method: Underground excavation of solidified salt
deposits (original bedded deposits or geological dome
formations).
Operational Environment: Salt mines are generally safe and
comfortable, maintaining an average temperature of ≈70°F year
-round.

Solution Mining and Manufactured Brine

Process Overview: Used to produce high-purity "Evaporated Salt".
1.Freshwater is injected into subterranean salt deposits.
2.Salt dissolves, creating a saturated brine solution.
3.Manufactured brine is pumped to the surface for purification and subsequent
forced evaporation/boiling.
Purity: Consistently achieves purity levels between 99.6% and 100%, ideal for
chemical feedstock and food-grade salt.
 Industrial Production and Uses of Iodized Salt
Purpose: Edible salt is iodized to ensure adequate dietary iodine nutrition.
Iodization Method: Dry mixing or spraying salt crystals with a fine solution.

Chemicals Used in Iodization

Chemical Required Amount Stability Note

Potassium Iodate (KIO3​) ≈57 grams per ton of salt Preferred globally for superior inherent stability.

Vulnerable to oxidation and evaporation; requires additives

Potassium Iodide (KI) N/A (requires stabilizers)
(dextrose, sodium thiosulfate).

Major Industrial Applications of Sodium Chloride

Industry Primary Use

Chlor-Alkali Indispensable raw material for producing chlorine gas and sodium hydroxide (caustic soda).

De-icing Used on roadways and infrastructure to lower the freezing point of water (snow/ice removal).

Water Treatment Integral to water softening processes and the regeneration of ion exchange resins.

Metallurgy Employed in high-temperature processes for the extraction of metals (e.g., aluminum, magnesium, titanium).
The Salt Recovery Process: Brine Purification Chemistry
Purpose: Rigorous pre-treatment to remove multivalent cations (Ca2+, Mg2+, Sr2+) that cause
contamination and increase processing costs.
Pre-treatment Sequence: High-purity brine relies on chemical precipitation.

Chemical Impurity Removal in Brine Pre-treatment

Target Impurity Key Chemical Process Reagent Used Resulting Precipitate

Calcium (Ca2+) &

Chemical Precipitation Sodium Carbonate (Na2​CO3​) Carbonate Salts (e.g., CaCO3​)
Strontium (Sr2+)
Chemical Precipitation/pH
Magnesium (Mg2+) Sodium Hydroxide (NaOH) Magnesium Hydroxide (Mg(OH)2​)
Increase

Suspended Solids Flocculation and Clarification Alum Dosing Settled Particulates

Final Tuning: Brine is often treated with acid to achieve a pH range of 5.5 to 6.9 before
crystallization.
Efficiency Strategy: A portion of the removed solids (like calcium carbonate) can be passed
back into the purification zone to optimize reaction efficiency and reduce chemical
consumption.
 Recovery and Finishing: Mechanical Separation and Refining
Separation: Crystallized salt must be separated from the mother liquor (bittern)
using high-efficiency mechanical separators.
Centrifugation: Pusher-type centrifuges are utilized for fine salt products to achieve
minimum moisture levels and maximize pure brine recovery.
Post-Processing :
1.Drying and screening to achieve uniform crystal size.
2.Conditioners and additives incorporated for "brilliant whiteness
and excellent free flowing properties".
3.Anti-caking agents (e.g., calcium silicate, sodium ferrocyanide) are
added to prevent clumping during storage.
Resource Recovery: The final concentrated bittern is often
processed further to produce other value-added products

Pusher-type centrifuge
Future Prospects and Sustainable Salt Production
Technological Integration (Extraction) :
Adoption of Automated drilling, remote-controlled machinery, and Artificial
Intelligence (AI).
Real-time monitoring and satellite data for optimization and environmental reporting.
Key Sustainability Trends :
Renewable Energy: Increasing use of solar and wind power
to meet ESG targets and reduce CO2​emissions.
Solution Mining: Environmentally favorable method with
minimal surface disturbance and controlled brine processing.

Zero Liquid Discharge (ZLD) Systems:

Zero Liquid Discharge (ZLD) Systems: Strategic investment to
recover nearly 100% of water and eliminate liquid effluent discharge. Zero Liquid Discharge
system
 Concluding Remarks and Strategic Outlook
Essential Resource: Salt remains critical for human health, food security, and as an
irreplaceable raw material for the massive chemical manufacturing sector.
Structural Challenge: Reconciling the growing demand for high-purity/specialty salts
with the high capital and operating costs of advanced purification and mass transfer
techniques.
Environmental Imperative: Rigorously addressing the environmental footprint,
specifically mitigating groundwater risks and optimizing the management of
concentrated brine effluent.
Strategic Focus: The future centers on continuous investment in:
Technological sophistication (automation and AI optimization).
Environmental responsibility (widespread adoption of ZLD and renewable energy
integration).
Market Outlook: Sustained global demand for industrial, de-icing, and specialty salts
ensures that technological and environmental evolution will continue to reshape salt
production practices.
THANK yOU