In chemical production, the crystallization and filtration of inorganic salt products, such as lithium carbonate, sodium sulfate, potassium chloride, and phosphates, serves as a core process. Though seemingly straightforward, this procedure poses substantial challenges: crystal particles are fragile and prone to breakage, the mother liquid features high viscosity, solid-liquid separation standards are stringent, and the materials are often corrosive or operated at elevated temperatures. Featuring a unique working principle and structural design, candle filters deliver remarkable advantages in the crystallization filtration of inorganic salts. They have become pivotal equipment for chemical enterprises to enhance product quality and reduce operating costs. This article elaborates on the application va

ue and technical highlights of candle filters in this typical working scenario.

Candle filters provide systematic solutions to the aforementioned challenges:

1. Fully Enclosed Operation to Eliminate Crystallization RisksOnce inorganic salt solution comes into contact with air, water evaporation easily causes surface crystallization, resulting in pipeline and euipment blockage. The fully enclosed structure of candle filters enables material operation under nitrogen protection or vacuum conditions, isolating contact with ambient air and effectively preventing unexpected crystallization and material oxidation.

2. Gentle Filtration to Protect Crystal IntegrityCandle filtration adopts an inside-out flow direction, allowing filter cakes to deposit evenly on the surface of filter cartridges. Without high-speed centrifugal force or extrusion shear force, it is particularly suitable for filtering acicular, flaky and fragile crystals. This maintains complete crystal morphology and improves overall product value.

3. Efficient Washing to Reduce Mother Liquid EntrainmentThe uniform and stable filter cake structure enables displacement washing. By introducing washing media such as purified water, solvents or saturated brine, the washing liquid penetrates the filter cake layer evenly and displaces the residual mother liquid between crystal particles. Compared with centrifuges, the washing efficiency increases by 20%~30% with less washing liquid consumption.

4. Dry Discharge to Cut Down Drying Energy ConsumptionAfter filtration, the filter cake is dewatered by compressed air or nitrogen. The moisture content of the filter cake can be controlled within 10%~20% depending on material characteristics, far lower than that of centrifuges (15%~30%) and plate-and-frame filter presses (25%~40%). This greatly reduces energy consumption in the subsequent drying process.

5. Excellent Cartridge Regeneration for Stable Long-Term OperationEquipped with sintered metal or precision wound wire filter cartridges and matched with a back-blow regeneration system, the filters restore full cleanliness after each slag discharge and avoid long-term clogging. The service life of filter cartridges generally reaches 3 to 5 years, ensuring low maintenance costs.

Analysis of Typical Application Scenarios

1. Crystallization and Filtration of Lithium Carbonate / Lithium Hydroxide

Background: New energy battery materials require extremely high purity of lithium salts (≥99.5% in general), with crystal particle size strictly controlled within a specific range.

Application Benefits

· Realizes efficient separation of mother liquid and crystals after carbonization and crystallization of lithium carbonate;

· Removes impurity ions such as Na⁺, K⁺ and SO₄²⁻ through 2 to 3 times of countercurrent washing;

· Controls filter cake moisture content ≤ 12%, allowing direct delivery to the drying process and reducing energy consumption by over 30%;

· Fully enclosed system prevents CO₂ escape and dust pollution.

2. Evaporation Crystallization Filtration of Ammonium Sulfate / Ammonium Chloride

Background: The coal chemical and fertilizer industries produce large quantities of by-product ammonium sulfate, which features fine crystal particles (20~100 μm) and high-viscosity mother liquid.

Application Benefits

· Intercepts particles above 5 μm, with filtrate clarity lower than 10 ppm for direct reuse or discharge;

· Adopts pre-coating and combined filtration mode to prevent fine particles from penetrating the filter cartridges;

· Supports automatic slag discharge, enabling direct packaging of dry filter cakes without secondary drying.

3. Phosphate Filtration (Dicalcium Phosphate, Potassium Dihydrogen Phosphate)

Background: Phosphate crystals tend to form acicular or flaky shapes, which are easily broken during centrifugation. Meanwhile, phosphate media bring strong corrosion to process equipment.

Application Benefits

· Adopts 316L or 2205 duplex stainless steel to resist corrosion caused by chloride and phosphate ions;

· Keeps the crystal integrity rate above 95%, delivering bright and high-quality crystals for higher market competitiveness;

· Reduces washing water consumption by 40% and lowers the burden of wastewater treatment.

4. Refining of Sodium Chloride and Anhydrous Sodium Sulfate

Background: Fine chemical production requires food-grade or pharmaceutical-grade inorganic salts, demanding deep washing for thorough impurity removal.

Application Benefits

· Achieves fully automatic cyclic operation including filtration, washing, dewatering and slag discharge;

· Increases the product purity of chloride and sulfate above 99.5% after precision washing;

· Adapts to high-temperature filtration at 80~100 ℃, perfectly matching thermal crystallization processes.

· Material Customization: 304, 316L, 2205, 2507 stainless steel and Hastelloy alloys are selected according to material corrosion resistance;

· Filtration Precision: Optional range from 5 μm to 100 μm to match different crystal particle sizes;

· Heat Preservation Design: Jacket insulation structure prevents blockage caused by high-temperature material crystallization;

· Modular Configuration: Filtration area ranges from 5 m² to 200 m², with single-unit or parallel multi-unit solutions to adapt to different production capacities.

If you are facing common difficulties in inorganic salt filtration, such as crystal fragmentation, incomplete washing, excessive energy consumption or increasing environmental pressure, please feel free to contact us. Supported by rich industry application experience, we will customize efficient, stable and cost-effective solid-liquid separation solutions, helping you strike an optimal balance between product quality and operating costs.