• Filter Cloth Selection: Horizontal Vacuum Belt Filter for Solid-Liquid Separation in Chromium Chemical Processing—Sodium Dichromate Filtration
  Filter Type: Horizontal Vacuum Belt Filter
  Application industry: Chemicals
  Material description: Sodium chromate
• Filter cloth manufacturer: Xiadis

In the chromium salt chemical industry, solid-liquid separation has always been a critical step determining product quality, energy consumption levels, and compliance with environmental protection standards. Particularly in the sodium chromate solution system—obtained by roasting, water leaching, and oxidative conversion of chromite ore—the slurry features high temperature, strong alkalinity, fine particle size, and the presence of unreacted materials and impurities. If filtration is not properly controlled, it will not only affect the efficiency of subsequent evaporation and crystallization processes but also increase the burden on the mother liquor circulation and place greater pressure on environmental treatment. Under these operating conditions, horizontal vacuum belt filters have become the mainstream choice for many chromium chemical enterprises, and the performance of the filter cloth matched to these machines directly determines the overall operational effectiveness of the entire system.

I. Specific Features of the Sodium Chromate Filtration Process

The production of sodium chromate typically involves high-temperature roasting followed by alkaline leaching. The resulting slurry exhibits the following notable characteristics:

1. Strong alkaline environment ： pH The value is generally in 10 The above points place high demands on the chemical resistance of filter cloths.
2. The temperature is slightly high. The slurry is often in 60℃ Above, some processes are even higher;
3. Wide particle size distribution It contains both coarse particulate residues and fine suspended solids;
4. The filter cake is significantly compressible. Under the action of vacuum negative pressure, a dense filter layer is easily formed.

Under these complex operating conditions, if the filter cloth is chosen improperly, common problems include: turbid filtrate, clogged filter cloth, difficult regeneration, high moisture content in the filter cake, and shortened operational cycles. Therefore, filter cloth is no longer simply a... “ Filter medium ” but rather the core functional component for the system’s stable operation.

II. Structure and Filter Cloth Matching Logic of Horizontal Vacuum Belt Filters

The horizontal vacuum belt filter continuously carries the slurry on a moving filter cloth, and under the negative pressure generated by the vacuum box, it achieves continuous filtration, washing, and dewatering. Its typical process includes: the fabric section. — Filtering area — Washing area — Drying zone — Discharge area. The filter cloth must not only perform the filtration task but also withstand repeated bending, tensioning, and high-frequency cleaning.

In the solid-liquid separation of sodium chromate, the following technical parameters should be given primary consideration when selecting filter cloth:

1. Retention accuracy and flux balance
   It is necessary to ensure both the clarity of the filtrate and to avoid excessively fine structures that could reduce the flux. A reasonably designed weaving structure can create a stable initial filter layer, leveraging... “ Secondary filtration of filter cake ” The principle is to improve efficiency.
2. Alkali resistance and antioxidant performance
   Chromium salt systems have a certain oxidizing property, so the filter cloth must maintain stable strength over long-term operation without becoming brittle or experiencing strength degradation.
3. Peeling performance
   The filter cake must detach smoothly in the discharge zone. If the surface structure of the filter cloth is improperly designed, it may cause adhesion and residue, thereby affecting the filtration process in the next cycle.
4. Dimensional stability
   Under conditions of sustained tension and temperature fluctuations, the warp and weft densities and thickness of filter cloths must be kept within a reasonable range; otherwise, sealing performance and vacuum efficiency will be affected.

III. Common Issues and Optimization Directions in Chromium Chemical Filtration

In actual operation, many enterprises encounter the following phenomena:

• The transparency of the filtrate is unstable.
• The filter cake has relatively high moisture content.
• The filter cloth has a relatively short lifespan.
• The energy consumption of the vacuum system has increased.

From a technical perspective, this is often not a single issue, but rather... “ Equipment — Filter cloth — Slurry ” This is due to insufficient matching among the three factors. For example, if the filter cloth has too low air permeability, although its retention performance will be good, the vacuum load will increase, leading to higher energy consumption. On the other hand, if the air permeability is too high, the clarity of the filtrate will be inadequate. Therefore, it is necessary to establish a parameter window tailored specifically for the sodium dichromate system based on experimental data.

Optimization directions typically include:

• Adjust the weaving structure to improve surface smoothness.
• Optimize the latitude-longitude density ratio and control pore distribution.
• Strengthen the surface treatment process to improve peel performance.
• According to different stages (coarse filtration) / Fine filtration) Configure differentiated filter cloths.

IV. The Value of Filter Cloth in Continuous Production

As the chromium salt industry gradually shifts toward larger-scale, continuous, and automated operations, the stability of the filtration process has become increasingly critical. Horizontal vacuum belt filters themselves offer advantages such as continuous operation, high filter cake washing efficiency, and excellent operational visibility. However, if the filter cloth quality is unstable, it can lead to frequent replacements and downtime for maintenance, directly impacting production capacity.

The value that high-quality filter cloth can bring includes:

• Increase the filtration rate and shorten the processing time per batch;
• Reduce the moisture content of the filter cake and decrease evaporation energy consumption.
• Improve the cleanliness of the filtrate and enhance the quality of crystallization.
• Extend the replacement cycle and reduce overall costs.

Against the backdrop of increasingly stringent carbon neutrality and environmental protection policies, filtration efficiency and energy consumption metrics have become critical components of corporate competitiveness. By optimizing filter cloth selection and operational parameters, not only can the burden of wastewater treatment be reduced, but also the utilization rate of chromium resources can be enhanced.

V. Future Trends: From “ Adaptation ” To “ Collaborative Design ”

In the future, the development direction of solid-liquid separation in chromium chemical processing will no longer be limited to improvements in single filter cloths or individual pieces of equipment; rather, it will move toward system-level, coordinated design. Specifically, during the equipment structural design phase, full consideration will be given to the operational characteristics of the filter cloth, ensuring a holistic match among the vacuum box structure, tensioning system, washing device, and filter cloth parameters.

Meanwhile, the introduction of digital monitoring technology will also provide real-time data support for the operational status of filter cloths. For example, by monitoring changes in differential pressure, filtration time curves, and trends in the turbidity of the filtrate, it is possible to detect filter cloth blockage or performance degradation in advance, enabling preventive maintenance.

VI. Conclusion

In the sodium dichromate production system, solid-liquid separation may seem like a conventional process step, yet it plays a decisive role in determining product purity, energy consumption control, and compliance with environmental standards. Thanks to its continuous and stable operation, the horizontal vacuum belt filter has become an essential piece of equipment in the chromium chemical industry, while the filter cloth is a critical component of this system. “ Functional Core ”。

Only by gaining a deep understanding of the interrelationships among slurry characteristics, equipment structure, and filter cloth parameters can we achieve truly efficient, stable, and low-consumption filtration results in high-alkali, high-temperature, and complex particle systems. For chromium chemical enterprises, filter cloth selection should not be limited to mere price comparisons; rather, it should be elevated to the strategic level of process optimization and system upgrades.

When filtering from “ Accessory Thinking ” Steering “ Systems thinking ” The potential for improving the solid-liquid separation efficiency and environmental protection levels of sodium chromate will far exceed conventional understanding.

Source: Xiadis | A leading domestic manufacturer of filter fabrics.