Diatomite, Diatomaceous Earth, Diatom Soil, Amorphous Silicon Dioxide, Kieselguhr, Filter Aid, Fossil Shell Flour, Siliceous Clay, Kizelgur

Diatomite, Diatomaceous Earth, Diatom Soil, Amorphous Silicon Dioxide, Kieselguhr, Filter Aid, Fossil Shell Flour, Siliceous Clay, Kizelgur

DIATOMITE (DIATOMACEOUS EARTH)

1. PRODUCT DEFINITION AND CHEMICAL IDENTITY

Note: Diatomite (diatomaceous earth) is a natural sedimentary rock composed of the fossilized siliceous shells (frustules) of microscopic aquatic algae called diatoms. Its high porosity, low density, and chemical inertness make it a versatile industrial material. It is available in various forms, including natural, calcined, and flux-calcined.

2. PHYSICAL AND CHEMICAL PROPERTIES

3. FUNCTIONAL PROPERTIES

• High Filtration Capacity: Used as a filter aid in the food, beverage, pharmaceutical, and chemical industries for clarifying liquids and retaining fine particles. The flux-calcined form, in particular, provides high flow rates and excellent clarity.

• Absorbency and Absorption: Its highly porous structure can absorb up to 1.5 times its own weight in liquid. It is used in cat litter, industrial spill cleanup, and as a carrier.

• Lightweight Filler and Insulation: Serves as a filler in lightweight concrete blocks, thermal and acoustic insulation boards in the construction sector.

• Natural Abrasive: Enters formulations as a gentle micro-abrasive in cosmetic and personal care products (peeling creams, toothpaste).

• Stabilizer and Anti-Caking Agent: Used in the explosives industry to stabilize sensitive components like nitroglycerin for dynamite production.

• Carrier and Flow Improver: Used as a carrier for active ingredients and an anti-caking agent in pesticides, paints, and coatings.

• Latex Coagulation Regulator: Particularly in latex processes like balloon production, it acts as a surface control and coagulation regulator.

4. ALTERNATIVE NAMES AND SYNONYMS

• Diatomite

• Diatomaceous Earth

• Kieselguhr / Kizelgur

• Filter Aid

• Fossil Shell Flour

• Siliceous Clay

• Diatom Soil

• Terre de diatomée (French)

• Natural Silica

5. PRODUCT TYPES AND TYPICAL SPECIFICATIONS

6. SECTORAL APPLICATIONS AND USAGE RATES

7. ALTERNATIVES AND COMPARISON

8. REGULATORY STATUS, SAFETY, AND STORAGE

• GHS Classification (CLP Regulation):

  • Signal Word: Not classified (for natural diatomite). It should be noted that uncalcined diatomite may contain crystalline silica and can cause lung damage if inhaled.

  • Calcined Diatomite: Cristobalite (crystalline silica) can form during calcination; in this case, the hazard statement H372 (Causes damage to organs through prolonged or repeated exposure if inhaled) is added. Inhaling calcined diatomite dust poses a serious health risk.

• Food Additive: Food-grade diatomite is used as a food processing aid and as an anti-caking agent in animal feed (FDA 21 CFR 573.340). It is permitted in food under the code E551 (Silicon Dioxide), although diatomite itself does not carry a direct E-code.

• Storage:

  • Store in a dry, cool, and well-ventilated area in tightly sealed packaging.

  • Protect from moisture; moisture can cause caking and microbial growth.

  • Rapid consumption is recommended after opening the packaging.

• Personal Protective Equipment (PPE):

  • Avoid breathing dust; use an appropriate dust mask (FFP2/FFP3).

  • Wear protective goggles and gloves.

  • Ensure adequate ventilation in the working area. A high level of protection is required, especially for calcined diatomite dust.

• Packaging: Typically sold in 25 kg kraft bags, 500 – 1000 kg big bags, or in bulk.

9. FREQUENTLY ASKED QUESTIONS

Q1: What is the difference between natural and calcined diatomite?
Natural diatomite has only been dried and milled; it retains its raw porous structure and amorphous silica form. Calcined diatomite has been heat-treated at 600-1000 °C. This process gives the product higher hardness, but a portion of the amorphous silica can transform into cristobalite (crystalline silica). Flux-calcined diatomite is treated with an alkali salt like soda ash before calcination and offers the highest filtration performance.

Q2: Why is inhaling diatomite dust dangerous?
Calcined diatomite, in particular, can contain crystalline silica (cristobalite), which can cause permanent lung damage if inhaled. Even natural diatomite, being a fine dust, can mechanically irritate the respiratory tract. Therefore, a suitable dust mask must always be worn when working with diatomite powder, and the work environment must be well-ventilated.

Q3: Can diatomite be used in food?
Yes, food-grade diatomite has undergone strict purity controls and can be used as a food processing aid (e.g., beer and wine filtration) and as an anti-caking agent in animal feeds. It can also be applied directly for insect control (in grain silos), but only products labelled as "food grade" should be used for this purpose.

Q4: What is the difference between diatomite and perlite?
Both are natural, amorphous silica-based materials used as filter aids and lightweight fillers. Diatomite is formed from fossilized algae, while perlite is formed from expanded volcanic glass. Perlite generally has a lower bulk density and provides a higher flow rate, while diatomite offers finer particles and higher clarity.

Q5: How should diatomite be disposed of?
Used diatomite (e.g., filter cake) should be disposed of in accordance with local regulations. It is generally classified as non-hazardous waste, but depending on the substances it contains (e.g., filtered chemicals), it may fall into the hazardous waste category. Bulk diatomite powder should not be poured into drains.

10. QUICK REFERENCE TABLE

TECHNICAL APPLICATION GUIDE: FILTRATION WITH DIATOMITE AND OTHER FILTER AIDS

This guide explains the principles of industrial liquid filtration, specifically focusing on how to apply diatomite (kieselguhr) and other filter aids (perlite, cellulose, etc.), the types of equipment used, and the fundamental operating procedures.

SECTION 1: FILTRATION PRINCIPLES AND FILTER TYPES

Diatomite and similar powders are used in filtration as "filter aids." The purpose is to form a permeable, porous "cake" layer on the surface of the primary filter (cloth, screen, membrane) to capture very fine particles and prevent the filter from clogging.

The main industrial filter types that work with filter aids are as follows:

1. Plate and Frame Filter Presses

• Operating Principle: The liquid is forced under high pressure through filter cloths clamped between a series of plates and frames. Solid particles and the filter aid build up a "cake" on the cloths.

• Advantages: Large filtration area, high cake capacity, easy cake removal.

• Typical Application: Liquids with high solids content, the beverage industry, chemical plants.

2. Rotary Vacuum Filters

• Operating Principle: A rotating drum is partially submerged in a vat of liquid. A vacuum is applied through the cloth on the drum's surface, drawing the liquid inward while solids accumulate on the drum surface. The cake is scraped off as the cycle completes.

• Advantages: Continuous operation, suitable for large volumes.

• Typical Application: Mining, wastewater treatment, large-scale chemical production.

3. Horizontal Leaf Filters

• Operating Principle: Filter elements (leaves) are arranged horizontally inside a vertical tank. These leaves, coated with filter aid, form a cake as the liquid passes through them.

• Advantages: Excellent cake stability (low risk of cake dropout), dry cake discharge.

• Typical Application: Beer, wine, edible oil filtration.

4. Vertical Leaf Filters

• Operating Principle: Filter elements positioned vertically inside a tank are used. The cake is typically cleaned by vibration or an air pulse after it has formed.

• Advantages: Compact design, suitable for automated cleaning.

• Typical Application: Chemical and pharmaceutical industries.

5. Candle Filters

• Operating Principle: Cylindrical, long "candle"-shaped filter elements are submerged in a tank. The liquid passes from the outside inward, and the cake forms on the outer surface of the element.

• Advantages: Very high filtration precision, closed system, ease of cleaning.

• Typical Application: Pharmaceuticals, fine chemicals, sterile filtration.

SECTION 2: APPLICATION OF DIATOMITE AND OTHER CHEMICALS (FILTER AIDS)

Filter aids are introduced into the filtration system using two main methods: Pre-coating and Body Feed. Typically, both are used together for the best results.

Step-by-Step Filtration Process:

1. Preparation: Fill a clean mixing tank with a clear liquid (water, solvent, or the filtrate itself). Slowly, while stirring, add the required amount of diatomite (or a perlite/cellulose blend) for pre-coating. Use a high-shear mixer to prevent lump formation.

2. Pre-coating: This suspension is pumped into the main filter unit and continuously circulated through the filter elements. This process continues until the liquid at the filter outlet is completely clear (typically 5-15 minutes). A protective diatomite cake has now formed on the filter elements.

3. Body Feed Filtration: Once pre-coating is complete, the main liquid feed is started. Simultaneously, the body feed (diatomite suspension) at the pre-determined rate begins to be dosed into the main liquid line or the filter inlet tank.

4. Filtration and Monitoring: The pressure difference (delta P) and flow rate are continuously monitored during operation. Thanks to the body feed, the pressure increase is slow and linear. Filtration is stopped when the pressure reaches the system's maximum limit or the flow rate drops to an unacceptable level.

5. Cake Removal: The filter is opened, and the accumulated cake (diatomite + captured solids) is cleaned mechanically (scraping, vibration) or by backwashing.

Comparative Application of Diatomite and Other Filter Aids:

• Diatomite: The most common and versatile filter aid. With its various particle size grades (fine, medium, coarse), it can be optimized to provide both high flow rates and excellent clarity. Flux-calcined diatomite, in particular, offers the highest performance.

• Perlite: Has a lower bulk density, so it forms a more voluminous cake for the same weight. Preferred in applications requiring very high flow rates, but the clarity it provides is not as high as diatomite.

• Cellulose Fibre: Due to its compressible nature, it is rarely used alone as a body feed. It is usually added to diatomite or perlite to strengthen the cake structure, prevent crack formation, and facilitate filter cleaning.

SUMMARY AND PRACTICAL RECOMMENDATIONS

1. Select the Right Material: Choose the correct diatomite/perlite grade (particle size) for your application. Use fine particle grades for high clarity and coarse particle grades for high flow rates.

2. Do Not Skip Pre-coating: Pre-coating extends the life of the filter elements and ensures easy cake release at the end of the filtration cycle. It is especially critical for plate and frame filter presses.

3. Optimize Body Feed: The body feed rate should be determined through laboratory tests based on the amount and type of solids in the liquid. Insufficient feeding leads to rapid clogging, while excessive feeding causes unnecessary cost.

4. Consider Blending: Both economical and high-performance filter aids can be prepared by blending pure diatomite, perlite, and cellulose fibres in appropriate ratios. For example, a mixture of diatomite and a small amount of cellulose prevents cake cracking.

5. Pay Attention to Suspension Preparation: For both pre-coating and body feed, the diatomite/perlite must be thoroughly mixed with sufficient liquid to prevent lump formation. Typically, stock suspensions of 10-20% (weight/volume) are prepared.