Silica Gel vs Calcium Chloride

Moisture can significantly damage products like electronics, food, and pharmaceuticals, causing items to degrade or spoil and leading to costly losses.

Therefore, it’s essential to use effective desiccant packaging solutions to protect products against moisture. Silica gel and calcium chloride are among the most popular desiccants for packaging.

In this article, we explore the differences between silica gel and calcium chloride as moisture adsorbers or absorbers so you can decide which to use for your applications.

What Is Silica Gel?

Silica gel is a natural desiccant and a porous, granular substance made from silicon dioxide with a high surface area that adsorbs water molecules very effectively. However, silica gel comes in various sizes and shapes, including small desiccant packs, beads, and powder form. It’s typically white, orange, or blue, changing colour upon saturation.

Silica gel applications:

• Moisture control inside product packaging, including electronics, leather goods, clothing, shoes, and food.
• Preserving documents and artefacts in archives, museums, and libraries by protecting them from moisture damage.
• Industrial uses, such as the drying and purification of gases and liquids, as well as the production of plastics, resins, and coatings.
• Protecting shipped products during transportation and storage by adsorbing excess moisture in packages and containers.
• Used in dehumidifiers to reduce the humidity level in indoor spaces.
• Incorporated into cat litter and other pet products as a moisture-adsorbing component.
• Silica gel can also preserve flowers and other organic materials.

What Is Calcium Chloride?

Calcium chloride is a chemical desiccant with a white, crystalline substance which is highly soluble in water and an effective moisture absorber due to its hygroscopic properties. Like silica gel, calcium chloride comes in different forms, including pellets, flakes, and powder.

The desiccant does not adsorb but absorbs moisture faster than silica gel in certain conditions, making it an excellent choice for quick-drying requirements. Calcium chloride can be mixed with polymer gelling agents and used as container desiccants to prevent container rain during shipping through different regions and climate changes.

Calcium chloride applications:

• De-icing and Snow Melting: Calcium chloride is commonly used as a de-icing agent for roads, sidewalks, and airport runways to melt snow and ice at low temperatures. It works by lowering the freezing point of water.
• Dust Control: It’s used to control dust on unpaved roads and in construction sites. The hygroscopic nature of calcium chloride helps to bind dust particles together.
• Construction: It’s used as a concrete accelerator for producing concrete, helping it to set faster.
• Increasing Fluid Drilling Density: Adding calcium chloride to drilling fluids can increase their density, helping to counteract high formation pressures and prevent wellbore instability.
• Shale Stabilisation: Calcium chloride can help maintain the stability of shale formations during hydraulic fracturing by preventing clay swelling and dispersion.
• Paper Industry: It’s used to improve the strength and quality of paper, including removing ink from recycled paper by breaking down the ink particles.
• Food Industry: Calcium chloride maintains the firmness of fruits and vegetables, enhances the texture of the cheese, and acts as a coagulant in the production of tofu.
• Water Industry: It’s used as a coagulant in water treatment processes, helping to remove impurities in water by destabilising suspended particles in water and causing them to clump together and settle out.
• Medical Applications: Calcium chloride is administered intravenously to treat severe hypocalcemia and counteract hyperkalemia’s harmful effects and is used as an antidote for magnesium toxicity.

How Do Silica Gel and Calcium Chloride Work?

Silica gel adsorb moisture from the air while calcium chloride absorb moisture into its internal structure. Unlike absorption – which is a physical process of one substance being absorbed into another – adsorption is a chemical process in which molecules adhere to the surface of another substance. When air containing moisture comes into contact with the surface of the adsorbent substance, the water molecules are attracted and held to its surface by forces of attraction.

Silica Gel Adsorption Process

Silica gel consists of tiny pores with a large surface area, allowing water molecules to be adsorbed. The water molecules are then trapped inside the pores of the silica gel, preventing them from causing damage to the surrounding environment. Once the silica gel has adsorbed a certain amount of moisture, it becomes saturated and can no longer adsorb additional water molecules.

At this point, the desiccant must be regenerated or replaced to continue its moisture-absorbing function. Regeneration of silica gel typically involves heating it to a high temperature (120°C), which removes the moisture and restores the desiccant to its original dry state.

Calcium Chloride Absorption Process

Calcium chloride is a hygroscopic salt that attracts water molecules through hygroscopy. Silica gel is also hygroscopic, but calcium chloride has a much higher absorption rate, especially in high-humidity environments. When exposed to moist air, calcium chloride absorbs water molecules through a physical process that involves dissolving the salt in the water it has attracted.

This process is also exothermic, which means that it releases heat. Therefore, calcium chloride can also be used as a de-icing agent, as the heat generated can help to melt ice and snow.

Once calcium chloride has absorbed significant moisture, the desiccant can no longer absorb additional water molecules and must be regenerated or replaced. Regenerating calcium chloride involves heating to remove moisture at 250°C for at least 1 hour . However, lower temperatures (47–58°C) are also recommended to improve longevity and performance.

Silica Gel vs Calcium Chloride: Adsorption or Absorption Capacity

Regarding absorption capacity, calcium chloride has a higher rate than silica gel which adsorbs moisture. Under 25°C and 70% relative humidity, calcium chloride can absorb significantly more moisture than silica gel. This desiccant’s high solubility in water also allows it to absorb moisture faster than silica gel.

However, silica gel works better in low-humidity conditions, making it a better option for long-term moisture control and smaller packaging. It retains the moisture inside itself, then releases it when heated and regenerated to be used again.

Silica Gel vs Calcium Chloride: Cost Comparison

Silica gel is generally more expensive than calcium chloride but more effective in certain applications. For example, it’s used in moisture-sensitive electronic equipment, where small amounts of moisture can cause significant damage. In comparison, calcium chloride is often used in large-scale moisture control applications, such as industrial settings or construction sites. In these applications, the lower cost of calcium chloride makes it a more cost-effective option, especially when large amounts of moisture must be removed quickly.

Furthermore, both silica gel and calcium chloride desiccant can be reused multiple times, which can help reduce their overall cost.

Silica Gel vs Calcium Chloride: Safety and Environmental Impact

Both silica gel and calcium chloride are generally safe to use but pose some risks:

• While generally non-toxic, food-safe silica gel can be harmful if ingested or inhaled. Therefore, bulk desiccants should always be kept away from children and pets.
• Blue silica gel also contains cobalt chloride, making it slightly toxic and unsafe for packaging consumables like foods and medicine.
• In comparison, calcium chloride can irritate the skin and eyes and release toxic fumes if exposed to high temperatures.

So, you should always follow proper safety precautions when handling these substances, such as wearing gloves, safety goggles, and a mask and keeping them out of reach of children and pets.

As to environmental concerns, silica gel is considered more eco-friendly than calcium chloride because it’s generally non-toxic and can be recycled. In contrast, calcium chloride can negatively impact soil and water quality if not disposed of properly or regenerated.

Conclusion

When choosing between silica gel and calcium chloride, the decision depends on your specific application:

• Calcium chloride is a fast-acting moisture absorber with a high absorption capacity and low cost, making it a good choice for large-scale moisture control applications.
• At the same time, silica gel is the better option for long-term moisture control, especially in low-humidity applications, such as preventing mould on shoes.

As you can see, both silica gel and calcium chloride are effective moisture adsorbers or absorbers that meet different packaging requirements. Choosing the right moisture adsorber or absorber is important if you want to protect your valuable products from humidity damage.

At Stream Peak, we provide extensive moisture packaging solutions, including silica gel packets and container desiccants. Our expertise extends to consulting on your packaging needs and enhancement strategies. Connect with our packaging engineers for collaboration opportunities for optimal solutions.