Industrial By-product Gypsum Solutions
What Is Borogypsum and What Grinding Solution Does It Need?
2026-09-08 16:18:19
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Borogypsum is a gypsum-containing industrial by-product from boric acid production. It is commonly formed when colemanite or another borate ore reacts with sulfuric acid, producing boric acid and calcium sulfate dihydrate. The filtered calcium sulfate-rich residue is called borogypsum.
Borogypsum can potentially be ground and reused, especially as a sulfate-bearing material for cement or selected construction products, but its boron content, silica, moisture, residual acidity and other impurities must be evaluated first. The suitable grinding solution depends on feed condition, required capacity, target fineness and final application. MTW European Grinding Mill, LM Vertical Roller Mill and Raymond mill can be considered after necessary material preparation.
How Borogypsum Is Generated
Borogypsum is associated with boric acid production from borate ores such as colemanite. In a typical process, colemanite reacts with sulfuric acid to produce boric acid in solution and calcium sulfate dihydrate as a solid residue.
A simplified reaction is:
2CaO·3B2O3·5H2O + 2H2SO4 + 6H2O → 6H3BO3 + 2CaSO4·2H2O
After the reaction mixture is filtered, the solid gypsum-containing filter residue is recovered as borogypsum. Research descriptions identify borogypsum as a material composed mainly of gypsum crystals together with boron oxide and other impurities generated during boric acid production from colemanite.
What Is Borogypsum Made Of?
The main component of borogypsum is usually calcium sulfate dihydrate, CaSO4·2H2O. However, unlike natural gypsum, it can also contain boron compounds, silica, residual boric acid, unreacted borate minerals, soluble salts, moisture and other source-specific constituents.
The composition depends on borate ore quality, acid-reaction conditions, washing efficiency, filtration performance and storage conditions. Published studies report widely different boron levels. One source describes borogypsum with approximately 11% B2O3 and trace lithium, while another cement-focused study reported approximately 1.5% B2O3 and 6.82% SiO2. These results are source-specific and show why representative analysis is essential before selecting a reuse route.
Before designing a grinding plant, test the actual material for:
Calcium sulfate dihydrate content
Free moisture and total moisture
Boron content, expressed as B2O3 or another relevant measure
Residual boric acid and pH
Silica, alumina, magnesium and other mineral impurities
Soluble salts and conductivity where relevant
Trace elements and other application-specific parameters
Particle-size distribution and maximum feed-lump size
Bulk density, flowability and tendency to compact
Target final application and customer quality limits
Why Borogypsum Needs Careful Evaluation
Borogypsum is not a uniform gypsum raw material. Its boron content and impurity profile can affect cement setting, gypsum hydration, calcination behavior, product strength, water demand and regulatory suitability.
Boron compounds may act as setting modifiers in cementitious and gypsum-based systems. This can be useful in controlled formulations, but variable boron content can make finished-product behavior difficult to predict. A material that is suitable for cement set regulation may not be suitable for white plaster, gypsum board or dry mortar.
Grinding does not remove boron, silica, residual boric acid or other chemical impurities. It mainly controls particle size and powder uniformity. Therefore, the material should be qualified for its intended application before it is ground into a commercial product.
Potential Reuse Applications
Suitable borogypsum may be evaluated for cement, construction materials, calcined gypsum products, mineral recovery and selected soil-related uses. The final route should be selected from material quality, treatment cost, product performance and local regulations.
Cement production
One of the most studied uses of borogypsum is as a calcium sulfate source for Portland cement. Gypsum is added to cement to regulate setting time, and borogypsum can potentially replace part of natural gypsum when its sulfate contribution and impurity profile are suitable.
Laboratory studies have reported that borogypsum can function as a cement set retarder. One study found that cement containing 5% borogypsum showed strength properties similar to cement made with natural gypsum, while increasing borogypsum from 5% to 7% increased setting time and reduced compressive strength. The same study found that 5% hemihydrate borogypsum developed higher 28-day compressive strength than the control mixture under the reported test conditions.
Another study reported that borogypsum could be used as a set retarder at up to 10% by cement weight in the tested system. These findings are not universal dosage recommendations. Actual cement performance depends on clinker mineralogy, cement fineness, gypsum form, boron content, impurity profile and the specific cement formulation.
Dry building mixtures and gypsum-based products
Borogypsum may be evaluated for dry building mixtures, gypsum-based composites, blocks and architectural products after appropriate treatment. A review of borogypsum as a secondary raw material identifies gypsum, anhydrite and silica in boric acid production waste as potential components for cement, dry building mixtures, gypsum boards and building products.
For these applications, the producer should test setting behavior, water demand, strength, dimensional stability, color, soluble-boron content and compatibility with additives. Boron-related effects can be important in formulations that contain cement, hemihydrate gypsum, lime, cellulose ethers or other chemical additives.
Calcined gypsum and plaster products
Borogypsum can be calcined to convert calcium sulfate dihydrate into hemihydrate gypsum. This may create a settable gypsum binder for plaster or other molded products. However, boron content and other impurities can alter calcination behavior, setting time and final product performance.
For plaster applications, product trials should measure phase composition, water demand, setting time, strength, color and long-term stability. If the target product is white decorative plaster, silica and boron-related impurities may limit suitability unless purification or blending is included.
Silica and boron recovery
Some borogypsum sources contain valuable boron, silica or trace lithium. Depending on composition and market conditions, the material may be evaluated for recovery of useful components before the gypsum fraction is used or disposed of.
Published work has considered borogypsum as a potential source of lithium through leaching, while other studies have proposed separation of silica concentrate from boric-acid production waste. These routes require specialized chemical or physical separation and should be assessed separately from a conventional gypsum grinding project.
Soil-related applications
Gypsum can provide calcium and sulfur for soils, and boron is also a plant micronutrient at low levels. However, boron can become harmful to plants when concentration or application rate is excessive. Borogypsum should not be used in agriculture without source-specific boron analysis, soil testing, crop evaluation and confirmation of local agricultural requirements.
Any soil application should consider soluble-boron release, soil pH, crop sensitivity, groundwater protection and long-term accumulation. Grinding can improve material dispersion, but it can also increase the rate at which soluble constituents become available.
Typical Borogypsum Processing Flow
A borogypsum processing line should be designed around the material and target product. For suitable prepared feed, a basic powder-production route may include:
Borogypsum receiving → sampling → covered storage → deagglomeration → dewatering or drying → grinding → classification → powder collection → storage or packing → quality control
If residual boric acid, soluble salts or other impurities must be managed, the route may include additional treatment:
Borogypsum receiving → sampling → segregation → washing / neutralization / separation when required → filtration and dewatering → drying → deagglomeration → grinding → classification → powder collection → application-specific testing
If the target product is calcined gypsum:
Prepared borogypsum → drying and grinding → controlled calcination → cooling → classification → finished-stucco storage → product testing
1. Receiving, Storage and Sampling
Borogypsum can be received as moist filter cake, loose material, compacted residue or stored stockpile feed. The receiving system should be designed to prevent rain exposure, uncontrolled moisture increase and contamination from soil or foreign material.
Covered storage is important because added moisture increases drying cost and can worsen lump formation. If the material quality varies by production batch or stockpile zone, the plant should use segregation or controlled blending before processing.
Sampling should represent normal operation. Test fresh material and stored material separately when their moisture, boron content or physical condition differs.
2. Washing, Neutralization and Impurity Management
Some borogypsum sources may require washing or neutralization before reuse. The need depends on residual boric acid, pH, soluble salts, boron concentration and final-application requirements.
Potential treatment measures include:
Water washing to reduce selected soluble constituents
Filtration and mechanical dewatering after washing
pH adjustment or neutralization where residual acidity is limiting
Physical separation or screening for coarse contamination
Flotation or mineral separation where silica recovery is economically justified
Controlled blending with compatible gypsum or mineral materials
Selection of a final application with suitable impurity tolerance
Washing should be evaluated carefully because it creates wastewater that may contain boron, dissolved salts and residual acid. A complete process design must include water recycling, filtrate treatment, solids handling and compliance planning.
3. Dewatering and Drying
Borogypsum may contain high free moisture after filtration. Mechanical dewatering should be evaluated first because it generally removes water at a lower energy cost than thermal drying.
After dewatering, drying may be required if the material remains too wet for stable grinding, classification, storage or final use. High moisture can cause bridging in hoppers, sticking on conveyors, coating of grinding components and caking of finished powder.
Drying should remove free moisture without unintentionally calcining the gypsum when the target product is calcium sulfate dihydrate powder. If the final product is hemihydrate plaster, calcination should be treated as a separate and controlled stage.
4. Deagglomeration and Feed Preparation
Even when borogypsum has fine primary particles, moist filter cake can form compacted lumps during filtration, storage and transport. Lump breaking, screening and controlled feeding create a more stable feed for the dryer and mill.
The feed system should be selected according to actual material behavior. Moist and cohesive borogypsum requires hoppers, feeders and transfer equipment designed to reduce bridging and buildup.
5. Grinding and Classification
Grinding produces borogypsum powder with controlled particle size for the intended application. For cement, the powder must provide stable sulfate dosing. For dry building mixtures, it must disperse uniformly and provide predictable setting behavior. For calcined gypsum products, it must support stable phase conversion and hydration performance.
For conventional industrial powder, an approximate range of 100–325 mesh may be considered as a starting point. The final specification should be determined through end-use testing and may include sieve residue, laser particle-size distribution, D50, D90, specific surface area and finished-powder moisture.
Classification separates qualified fine powder from oversized material. Stable airflow, feed rate and classifier settings help maintain product consistency and reduce unnecessary grinding energy.
Grinding-Mill Selection for Borogypsum
MTW European Grinding Mill, LM Vertical Roller Mill and Raymond mill can be considered for suitable borogypsum after material evaluation and feed preparation.
MTW European Grinding Mill
MTW European Grinding Mill is suitable for small-to-medium capacity borogypsum powder projects with prepared, relatively stable feed. It can produce controlled conventional fineness when moisture is manageable and the material has been deagglomerated or dried as required.
For wet borogypsum filter cake, upstream dewatering and drying are normally needed before MTW grinding. The mill provides particle-size control but does not remove boron, silica, residual acidity or other chemical limitations.
LM Vertical Roller Mill
LM Vertical Roller Mill is suitable for medium-to-large capacity borogypsum processing and projects with significant drying demand. It can integrate drying, grinding and classification when a suitable heat source is available and the process is designed around actual feed moisture.
It is especially relevant for continuous high-output powder production from moist borogypsum. The final design should consider moisture variation, evaporation load, target fineness, boron-related quality requirements and finished-powder capacity.
Raymond Mill
Raymond mill can be considered for conventional borogypsum powder production with moderate output requirements and dry or pre-dried, stable feed. It is generally suitable where the project does not require major integrated drying duty.
For moist, sticky or variable borogypsum, the process should improve dewatering, drying and feed conditioning before a Raymond mill is selected.
Borogypsum Grinding vs. Calcination
Grinding and calcination have different purposes. Grinding reduces particle size and produces controlled borogypsum powder. Calcination removes part of the chemically bound water from calcium sulfate dihydrate and converts it into calcium sulfate hemihydrate.
Use grinding only when the final product is dihydrate gypsum powder for cement, dry mixtures or another qualified use. Add controlled calcination when the product requires a settable gypsum binder for plaster, blocks, boards or molded gypsum products.
Borogypsum should be tested before calcination because boron content and other impurities can affect phase conversion, setting time, water demand, strength and product stability. The target product must be confirmed before the thermal process is selected.
Quality Control for Reused Borogypsum
Quality control should cover both incoming material and finished powder. The test plan should match the selected end use and the expected variability of the boric acid production source.
Typical quality-control items include:
Calcium sulfate content and gypsum phase
Free moisture and finished-powder moisture
Boron content and soluble-boron level where relevant
Residual boric acid and pH
Silica, alumina and other mineral impurities
Soluble salts and conductivity
Particle-size distribution and sieve residue
Bulk density and powder flowability
SO3 contribution and cement setting behavior for cement applications
Setting time, water demand and strength for gypsum-based products
Leaching and environmental parameters where required
Common Challenges in Borogypsum Reuse
Variable boron content
Boron content can vary with ore quality and production conditions. This can change cement setting time, gypsum hydration behavior and the suitability of the material for different applications. Regular sampling and source control are important.
Residual boric acid and acidity
Residual boric acid or low pH can affect equipment corrosion, handling safety and compatibility with cementitious products. If acidity is outside the target range, washing, neutralization, blending or another treatment route may be required.
Silica and mineral impurities
Silica and other non-gypsum minerals can reduce gypsum purity, alter powder behavior and increase wear on grinding components. In some sources, silica recovery may be economically attractive; in others, it is simply a quality-control issue.
High moisture and difficult handling
Moist borogypsum filter cake can compact, bridge and stick to handling equipment. Dewatering, covered storage, lump breaking and thermal drying may be needed before stable grinding is possible.
Using grinding as a substitute for material treatment
Grinding cannot remove boron, residual acidity, soluble salts or silica. If the powder fails end-use testing, the solution may require source-process improvement, washing, neutralization, blending, mineral recovery or selection of a different reuse application.
Recommended Project Sequence
Identify the boric acid production route and borogypsum source.
Collect representative samples from normal production and storage conditions.
Test gypsum content, moisture, boron content, pH, silica, soluble salts and physical condition.
Define the intended final application and its acceptance requirements.
Determine whether washing, neutralization, dewatering, drying, blending or mineral separation is required.
Set target fineness, finished-powder moisture and required production capacity.
Select MTW European Grinding Mill for prepared small-to-medium capacity powder production.
Select LM Vertical Roller Mill for high-capacity production or integrated drying requirements.
Select Raymond mill for conventional processing with dry, stable and adequately prepared feed.
Add calcination only if the target product requires hemihydrate gypsum.
Validate the finished material through cement, mortar, plaster or other end-use trials.
Maintain routine quality control for feed material and finished product.
Conclusion
Borogypsum is a calcium sulfate-rich by-product of boric acid production from borate ores. It can potentially be reused in cement, dry building mixtures, gypsum-based materials and other industrial applications, but its boron content, residual acidity, silica, moisture and source-specific impurities must be tested before processing.
For suitable material, the processing line can include dewatering, drying, deagglomeration, grinding, classification, powder collection and quality control. MTW European Grinding Mill is suitable for prepared small-to-medium capacity projects. LM Vertical Roller Mill is suitable for larger-capacity systems and materials requiring integrated drying. Raymond mill is suitable for conventional powder production with dry, stable and properly conditioned feed.
Grinding provides particle-size control, not impurity removal. The most reliable borogypsum reuse project begins with representative material analysis, defines a qualified final application and includes any necessary treatment before powder production.
