NEWS
Focus On High-Quality Silicate (Ceramic) Materials
Using Recycled Materials in Ceramic Body: Challenges and Dispersant Solutions
By Goway Chemical Technical Team | Updated June 2026 | For Ceramic Tile Engineers & Procurement Teams
Key Takeaways
- Ionic contamination is the #1 destabilizer. Recycled body waste routinely leaches Ca²⁺, Mg²⁺, and SO₄²⁻ into slurry water. These ions reduce the Zeta potential of clay particles, triggering flocculation and raising apparent viscosity. INSIGHT
- Surface area increase amplifies dispersant demand. Finer fractions from size reduction of recycled material increase specific surface area (SSA), meaning more dispersant molecules are needed per unit weight to achieve equivalent coverage. Typical dosage recalibration is required when substitution exceeds approximately 10% of dry body weight. (Industry observation; verify under your conditions.)
- STPP sensitivity to Ca²⁺ / Mg²⁺ is a recognized limitation. In high-calcium or high-magnesium recycled systems, phosphate-based dispersants may lose effectiveness due to competitive precipitation. Evaluating a ceramic deflocculant with chelating or silicate-type chemistry is worth testing. APPLICATION
- Organic residues require separate assessment. Binder and coating residues in recycled powder can cause foaming, increase apparent thixotropy, and reduce batch consistency. LOI (Loss on Ignition) testing is a practical first-line indicator.
- Pre-treatment and controlled substitution ratios are the most reliable risk management tools. Chemical solutions address symptoms; pre-treatment and formulation discipline address root causes. A combined approach typically produces the most stable outcome.
1. Why Recycled Body Materials Cause Slurry Problems
Ceramic production lines generate substantial volumes of waste body material — including green-body trimmings, dry-pressing rejects, glaze-line scrap, and post-kiln fragments. The economic rationale for recycling these materials back into the slurry batch is clear: reduced raw material cost, lower waste disposal burden, and improved overall yield.
However, recycled body waste is chemically and physically different from virgin raw materials. Over its service life in the production process, body material accumulates contaminants, undergoes partial thermal or chemical transformation, and acquires a different particle size distribution compared to its starting ingredients. When reintroduced into a fresh slurry, these accumulated differences can disrupt the carefully balanced colloidal system that gives the slurry its target rheological properties.
The three primary disruption mechanisms — ionic contamination, surface area changes, and organic residues — interact with each other and with the existing dispersant system in ways that can be difficult to predict without targeted characterization. This guide addresses each mechanism separately, then provides a framework for selecting and applying dispersant solutions.
Ionic Contamination
Ca²⁺, Mg²⁺, SO₄²⁻ ions leach from recycled material, compressing clay double layers and causing flocculation.
Surface Area Increase
Mechanical comminution and fine fraction accumulation raise SSA, increasing dispersant demand per unit weight.
Organic Residues
Binder burn-off products and coating residues interfere with rheological behavior and may cause persistent foaming.
2. Challenge 1: Ionic Contamination — Zeta Potential Disruption
The Mechanism
Clay minerals in ceramic body carry a negative surface charge in aqueous suspension. This charge creates an electrostatic repulsion between particles — a stabilizing force that keeps the slurry fluid. The strength and extent of this repulsion is characterized by the Zeta potential (ζ), typically measured in millivolts. In a well-dispersed ceramic slurry, Zeta potential is commonly targeted in the range of −30 mV or below (more negative = more stable), though exact thresholds depend on solid content and clay system. (Industry reference values; verify under your specific conditions.)
Recycled ceramic body waste — particularly from kiln-fired fragments and glaze-line scrap — can introduce elevated levels of Ca²⁺, Mg²⁺, and SO₄²⁻ ions into the slurry water as the material dissolves or hydrates. These multivalent cations interact strongly with the negative clay surfaces, compressing the electrical double layer (the Stern + diffuse layer surrounding each particle). This effect, described quantitatively by DLVO theory, reduces the effective repulsion range between particles. When the double layer is sufficiently compressed, particles can approach close enough for van der Waals attractive forces to dominate, leading to flocculation.
Practical Consequences of Ionic Contamination
- Apparent viscosity increases at constant solid content — often manifested as longer Ford Cup flow times
- Thixotropy increases — the slurry becomes more gel-like at rest and requires more energy to re-fluidize
- Dispersant efficiency drops — the same dosage of STPP or deflocculant produces less fluidity because a larger proportion is consumed competing with flocculating ions
- Batch variability increases — recycled material batches may differ in ionic load, making slurry behavior less predictable
Ion Sources in Common Recycled Materials
| Recycled Material Type | Likely Ionic Contaminants | Primary Source | Risk Level |
|---|---|---|---|
| Green body trimmings (unfired) | Low ionic load; mainly fine particle fraction risk | Processing water, raw material impurities | LOW |
| Dry-press powder rejects | Low to moderate; possible SO₄²⁻ from binders | Binder decomposition products | MODERATE |
| Bisque-fired (pre-glaze) scrap | Ca²⁺, Mg²⁺ released on re-hydration | Partial decomposition of calcium-containing minerals | HIGH |
| Glaze-line scrap (with glaze remnants) | Ca²⁺, Pb²⁺ (if applicable), Ba²⁺, SO₄²⁻ | Glaze raw materials (calcium carbonate, barium carbonate, frit) | HIGH |
| Post-kiln production waste (fired) | High Ca²⁺, Mg²⁺; possible glass-phase dissolution | Fired mineral phases, frit residues | HIGH |
Note: Ion type and concentration are indicative based on typical production scenarios. Actual contamination levels depend on body formulation, firing temperature, glaze composition, and recycling handling conditions. Always characterize your specific recycled material stream before formulating a dispersant response.
Diagnosis: How to Identify Ionic Contamination as the Root Cause
Before adjusting your dispersant system, confirm that ionic contamination is the primary driver. Practical indicators include:
- Ford Cup flow time increases proportionally with recycled material addition ratio — suggests systematic slurry loading effect
- Slurry pH drops following recycled material addition — may indicate dissolution of acidic mineral phases
- Increasing dispersant dosage provides diminishing returns — characteristic of ionic competition with dispersant adsorption sites
- Water conductivity test on recycled material extract: dissolve 10 g of recycled powder in 100 mL deionized water, stir for 5 minutes, filter and measure electrical conductivity. Values significantly above the virgin material control suggest elevated ionic load. (Field practice; threshold values are process-specific.)
3. Challenge 2: Fine Particles — Surface Area & Water Demand
Recycled ceramic body materials are typically subjected to size reduction processes — jaw crushing, ball milling, or grinding — before re-incorporation into slurry. These processes generate a higher proportion of fine and ultrafine particles compared to the original raw materials. Additionally, accumulated fines from production (conveyor dusts, overflow powder) that are collected and recycled carry a naturally fine particle distribution.
Why Fine Particles Change Slurry Behavior
Specific Surface Area (SSA) is inversely proportional to particle size. As recycled material introduces finer particles, the total surface area per unit mass of dry body increases. This creates two related process effects:
| Parameter | Direction of Change | Practical Consequence |
|---|---|---|
| Specific Surface Area (SSA) | ↑ Increases | More dispersant molecules required to achieve the same surface coverage density per unit weight |
| Free water demand | ↑ Increases | Higher water-to-solid ratio needed to achieve target slurry flowability, or solid content must be reduced |
| Spray drying yield | ↓ Decreases (potential) | Higher water content requires more evaporation energy; drying efficiency may decline |
| Thixotropy index | ↑ Increases | Slurry may become more gel-like at rest, increasing risk of pipeline sedimentation and pump blockage |
| Green body dimensional stability | Variable | Finer particle packing may affect shrinkage behavior during pressing and firing; requires verification |
Practical Threshold: Substitution Ratio and SSA Impact
In many tile body operations, substitution levels up to approximately 5–10% of dry body weight of green-body scrap can often be managed with incremental dispersant dosage adjustments, provided the recycled material has been sized to be consistent with the original formulation. Beyond this range — particularly when incorporating fired or bisque-fired scrap — the SSA and ionic effects compound, typically requiring more systematic reformulation.
These substitution thresholds are indicative based on typical production observations and do not represent guaranteed performance levels. Your process-specific limit should be established through controlled incremental trials.
4. Challenge 3: Organic Residues — Rheology Disruption & Foaming
Ceramic body formulations commonly contain organic additives — binders, waxes, release agents, temporary plasticizers, and in some cases, organic polymeric binders such as those in the Organic Polymeric Binder category (e.g., FG-ZM01D, FG-ZM01A from Goway's product range). When body material is recycled without sufficient pre-calcination to decompose these organics, residual organic matter enters the slurry system.
How Organic Residues Affect Slurry
- Surface-active organic fragments (from partial polymer decomposition) can adsorb onto clay particle surfaces, competing with or displacing dispersant molecules and altering surface chemistry in unpredictable ways
- Foaming is a common symptom when amphiphilic organic fragments are present. Persistent surface foam on the slurry can trap air, reducing slurry density consistency and creating green body defects
- Thixotropy may increase abnormally if organic matter forms weak gel networks between particles, increasing the energy required to maintain flow
- Dispersant dosage response becomes non-linear — organic contamination changes the adsorption isotherms of conventional ionic dispersants, making it difficult to predict optimal dosage through standard methods
LOI as a Preliminary Screen
Loss on Ignition (LOI) testing of recycled powder at 600°C (to decompose organics without calcining carbonates) provides a practical first-line indicator of organic load. A significantly elevated LOI compared to virgin material suggests organic residue is present at a level worth addressing before slurry incorporation.
LOI thresholds that define "acceptable" organic load are body-formulation specific and must be established through your own process characterization. We recommend establishing a control baseline with virgin material before evaluating recycled material.
5. Solution Mechanisms: How Dispersants Address These Challenges
Ceramic dispersants — including Sodium Tripolyphosphate (STPP), compound ceramic deflocculants, and Sodium Hexametaphosphate (SHMP) — stabilize slurry through different primary mechanisms. Understanding these mechanisms is essential for selecting the right approach when recycled materials are involved.
| Dispersant Type | Primary Mechanism | Response to Multivalent Ions (Ca²⁺, Mg²⁺) | Key Limitation in Recycled Systems |
|---|---|---|---|
| STPP (e.g., FG-1003) | Phosphate adsorption onto clay surfaces → electrostatic repulsion; sequestration of some cations via complex formation | Moderate; can form calcium/magnesium phosphate precipitates when Ca²⁺/Mg²⁺ levels are elevated, reducing effective dispersant concentration | Efficiency drops significantly when Ca²⁺ load from recycled material exceeds the sequestration capacity; may require higher dosage or formulation adjustment |
| Ceramic Deflocculant (compound type; e.g., FG-2017, FG-MK03, FG-N203B, FG-SL01A) | High NaO content provides Na⁺ ion exchange and electrostatic repulsion; silicate components (where present) contribute steric and electrostatic effects; multi-component synergy | Generally broader ionic tolerance than pure STPP; silicate components may form less-soluble complexes than phosphate, maintaining dispersion in moderate-calcium systems | Optimal dosage must be determined under actual recycled-material conditions; cannot fully neutralize very high ionic loads without pre-treatment |
| SHMP (Sodium Hexametaphosphate) | Strong chelation of multivalent cations (Ca²⁺, Mg²⁺) into soluble complexes, preventing them from compressing the clay double layer | High; chelation is the primary function — SHMP directly addresses ionic contamination by sequestering interfering ions before they interact with clay surfaces | Hydrolysis over time in slurry (especially at elevated temperature or pH); generally used as a complementary component rather than sole dispersant |
| STPP + SHMP Combination | Synergistic: SHMP sequesters Ca²⁺/Mg²⁺ while STPP provides ongoing surface adsorption and electrostatic stabilization | High combined performance; SHMP reduces the cation load that would otherwise compete with STPP adsorption | Requires careful ratio optimization; over-use of either component can affect slurry pH, viscosity, and green body properties |
Source (Goway product data): FG-2017: NaO 30–32%, P₂O₅ 0–1% (Source: Goway Technical Data Sheet). FG-MK03: NaO 12–15%, SiO₂ 20–22%, P₂O₅ 1–2% (Source: Goway Technical Data Sheet). FG-N203B: NaO 15–18%, SiO₂ 30–33% (Source: Goway Technical Data Sheet). FG-SL01A: NaO 18–20%, SiO₂ 18–20% (Source: Goway Technical Data Sheet). STPP FG-1003: Na₅P₃O₁₀ 94%, P₂O₅ 56%, Fe₂O₃ 0.015%, pH 8.0–9.0 (Source: Goway Technical Data Sheet). SHMP data not from Goway TDS; refer to manufacturer documentation.
Why Deflocculant Multi-Component Chemistry May Offer Broader Tolerance
Compound ceramic deflocculants from Goway's product range — such as FG-MK03 and FG-N203B — contain both high-NaO components and SiO₂-containing components (NaO 12–15% with SiO₂ 20–22% for FG-MK03; NaO 15–18% with SiO₂ 30–33% for FG-N203B). The silicate fraction may contribute steric hindrance effects in addition to electrostatic stabilization, which can maintain particle separation under conditions where purely electrostatic mechanisms begin to fail due to ionic competition.
However, the advantage of compound deflocculants over STPP in recycled-material systems is not absolute. It depends on the specific ionic species, their concentration, the clay system's natural surface chemistry, and the overall slurry pH. Comparative trials under your actual conditions remain the only reliable way to determine which approach is most effective.
For a detailed performance comparison between STPP and ceramic deflocculants across multiple dimensions, see our full data-driven guide: STPP vs Ceramic Deflocculant: Cost & Performance Guide.
6. Selection & Dosing Matrix
The following matrix provides a starting framework for selecting a dispersant approach based on the primary challenge identified through characterization. All dosage ranges are starting points for laboratory evaluation — final dosage must be determined through your five-point dosage curve under actual production conditions.
| Primary Challenge Identified | Recommended Starting Approach | Goway Product(s) to Evaluate | Typical Starting Dosage Range | Key Trial Measurement |
|---|---|---|---|---|
| Moderate ionic load (≤10% recycled green body scrap, low Ca²⁺ source) | Incremental increase of existing STPP dosage | FG-1003 (STPP, Na₅P₃O₁₀ 94%) | Increase from baseline by 10–20% of current dosage; verify specific gravity | Ford Cup flow time vs. dosage curve; pH |
| High ionic load (bisque-fired scrap, glaze-line waste, post-kiln fragments) | Switch to compound ceramic deflocculant or use STPP + SHMP combination | FG-2017, FG-MK03, FG-N203B, or FG-SL01A | Establish 5-point dosage curve from 0.1–0.5% on dry body weight as starting bracket; adjust based on Ford Cup response | Ford Cup, thixotropy (2-min rest test), Zeta potential if available |
| Surface area increase (fine particle fraction, comminuted scrap >15% substitution) | Reformulate total dispersant quantity based on new SSA estimate; consider a deflocculant with strong surface coverage efficiency | FG-MK03 or FG-N203B (SiO₂-containing grades for broader surface interaction) | Recalculate based on surface area increment; start 20–30% above original dosage per unit dry body | Particle size distribution (D50, D90); Ford Cup at multiple solid contents |
| Organic residues (foaming, abnormal thixotropy) | Pre-treatment (calcination of recycled material) as primary response; dispersant optimization secondary | After pre-treatment: reassess with standard deflocculant range | Pre-treat at 550–650°C before re-assessing dispersant need | LOI before and after calcination; foam index after slurry preparation |
| Mixed challenges (common in industrial scrap streams with multiple source types) | Systematic isolation protocol: characterize each challenge independently before combining solutions | STPP + SHMP combination as first trial; evaluate ceramic deflocculant grades as alternative | Start SHMP at 0.05–0.15% on dry body weight in combination with current STPP dosage | Full slurry parameter set: Ford Cup, specific gravity, pH, foam, thixotropy, green strength after drying |
Dosage ranges are general starting brackets for laboratory trials, not guaranteed optimal levels. All performance claims regarding Goway products are based on product TDS specifications, not on measured performance in recycled-body systems specifically. Final dosage and product selection must be validated through your own plant trials. (Source for product parameters: Goway Technical Data Sheet)
7. Pre-Treatment and Substitution Ratio Guidance
Chemical dispersant adjustments treat the symptoms of recycled-material contamination. Pre-treatment and controlled substitution address the root causes. The most reliable outcomes are achieved by combining both approaches.
Pre-Treatment Options
| Pre-Treatment Method | Primary Challenge Addressed | Practical Considerations | Limitations |
|---|---|---|---|
| Dry classification / screening | Surface area / fine particle fraction | Remove particles above D90 target before incorporation; combine with size reduction control to maintain consistent PSD | Does not address ionic or organic contamination; adds processing step |
| Calcination at 550–700°C | Organic residues | Decomposes organic binders and coatings; LOI test before and after to verify effectiveness; avoid temperatures that would initiate significant crystalline phase changes | Energy cost; may increase surface reactivity; does not remove ionic contaminants from fired scrap |
| Pre-washing / water leaching | Soluble ionic contamination (Ca²⁺, Mg²⁺, SO₄²⁻) | Wash recycled powder with deionized or soft water before incorporation; monitor wash-water conductivity to track extraction efficiency | Water consumption; requires drying step or slurry water management; may not remove tightly bound ionic species |
| Pre-dispersion slurry | Consistent incorporation of recycled fines | Pre-disperse recycled material in a small volume of water with dispersant before adding to main batch; ensures homogeneous distribution and surface wetting before mass slurry contact | Requires separate mixing equipment; adds batch preparation complexity |
Controlled Substitution Ratio Protocol
Rather than setting a fixed substitution ratio target from the start, we recommend an incremental approach:
- Characterize baseline: Measure Ford Cup flow time, specific gravity, pH, and thixotropy of the current virgin-material slurry formulation at the target solid content.
- Start at 5% substitution: Replace 5% of dry body weight with recycled material. Re-measure all baseline parameters.
- If stable, increase to 10%: Repeat at each increment of approximately 5%, documenting the dispersant dosage adjustment required to maintain target slurry parameters.
- Identify the inflection point: The substitution level at which dispersant dosage adjustment alone can no longer maintain acceptable slurry parameters — or where pre-treatment becomes necessary — defines your process-specific limit.
- Validate green body properties: At your target substitution ratio, verify that dry green strength and drying shrinkage remain within acceptable ranges. See our guide on improving ceramic green body strength for related considerations.
8. Lab Trial Protocol
The following protocol is designed for in-plant laboratory evaluation of dispersant performance with recycled body materials. It assumes access to a Ford Cup (FC4 or FC6), a precision balance, a standard slurry mixer, and basic pH/conductivity meter.
-
Establish the Control Baseline
Prepare 2 kg of virgin-material slurry at your target solid content (typically 62–66% by weight for tile body). Measure: Ford Cup flow time (FC4), slurry specific gravity (SG), pH, and note thixotropy by measuring flow time at 0 min and 5 min of rest. This is your reference point.
-
Characterize Recycled Material
Measure LOI of recycled powder at 600°C (organics indicator) and at 1000°C (total). Conduct conductivity test of 10 g / 100 mL deionized water extract. Measure D50/D90 by laser diffraction if available. Document material source and any known contamination history.
-
Prepare Recycled-Material Slurry at Target Substitution
Prepare the same 2 kg batch replacing 5% of dry body weight with recycled material. Use the same dispersant type and dosage as the baseline batch. Measure all baseline parameters. Document the difference from control.
-
Run Five-Point Dispersant Dosage Curve
Prepare five batches with dispersant dosage at 0.1×, 0.5×, 1×, 1.5×, and 2× the control dosage (or your chosen bracket). Record Ford Cup flow time for each. Identify the dosage that achieves target flow time. Calculate the dosage increment needed versus the virgin-material baseline.
-
Evaluate Alternative Dispersant (if STPP response is insufficient)
If the five-point curve indicates that STPP requires a dosage increment greater than approximately 40% to maintain target flow time, or if thixotropy remains elevated even at higher dosage, prepare a parallel set of batches using a ceramic deflocculant (e.g., FG-2017 or FG-MK03 from Goway's deflocculant range). Run the same five-point curve and compare flow time vs. dosage efficiency. Document cost per ton of body for comparison.
-
Validate Green Body Properties
Using the selected dispersant and dosage, spray-dry or slab-press test specimens. Measure green body density, drying shrinkage (%), and MOR (Modulus of Rupture) on dried specimens (n ≥ 5 per condition per GB/T 3810 reference method or equivalent). Compare against virgin-material baseline. If green strength drops more than approximately 10% from baseline, additional binder system evaluation may be warranted.
-
Scale Incrementally to Target Substitution Ratio
If 5% passes all validation criteria, repeat Steps 3–6 at 10%, then 15%, incrementally. At each step, document: dispersant dosage required, additional cost per ton, and any change in green body or fired properties. Establish a documented process window with upper/lower dispersant dosage limits and a maximum recycled material ratio specification.
9. Troubleshooting Guide
The following troubleshooting cases cover the most common symptoms encountered when incorporating recycled body materials.
10. Frequently Asked Questions
Request a Customized Dispersant Solution for Your Recycled Body Application
Every recycled material stream is different. Goway's technical team can review your specific situation and recommend a targeted dispersant evaluation plan.
To help us provide a relevant recommendation, please share:
- Recycled material source type (green body scrap / bisque-fired / post-kiln fragments / glaze-line waste)
- Current substitution ratio or target ratio
- Specific slurry problem experienced (viscosity increase / foaming / thixotropy / strength loss)
- Current dispersant type and dosage in your virgin-material baseline formula
- Optional: LOI and conductivity test results if available
We can also coordinate a free preliminary evaluation of your recycled material sample to assist in formulating a targeted response.
Submit Your Recycled Material Parameters →Technical Notes & Data Sources
Product Data (P1 — Goway TDS): All Goway product parameter values cited in this article are sourced from Goway Technical Data Sheets (TDS) as compiled in the internal product database (v2.1, updated 2026-05-14): FG-2017, FG-MK03, FG-N203B, FG-SL01A (Ceramic Deflocculant range); FG-1003, FG-N5, FG-N8, FG-N9 (STPP range). Data verified by Goway Product Team.
Mechanism and Process Guidance (P2 — Industry Science): Descriptions of Zeta potential, DLVO theory, ionic double layer compression, and SSA effects on dispersant demand are based on established colloidal chemistry principles, consistent with references including ASTM C326, ISO 10545 series, and standard ceramic engineering literature. These are not proprietary claims.
Substitution Ratios and Thresholds (P3 — Industry Observation): Substitution ratio guidance (5–10–20% ranges) and LOI threshold references represent commonly cited operational parameters in tile body manufacturing literature and field observations. They are not Goway-measured data points. They are provided as a starting context only.
Mandatory Disclaimer: All dispersant selection, dosage, and pre-treatment guidance in this article is general in nature and does not constitute a guarantee of performance in your specific application. Recycled material characteristics vary significantly by source, production history, and handling conditions. Final parameters should be verified against the latest batch COA and through laboratory trials under your actual process conditions. Industrial-scale changes should only be implemented after validation at laboratory and pilot scale. Goway accepts no liability for outcomes resulting from application of this guidance without proper site-specific validation.
Evidence Tier Summary:
- A-Level (Tier A — Measured Data): Goway product parameters (TDS source)
- B-Level (Tier B — Application Guidance): Dispersant selection framework; dosage starting ranges; trial protocol steps
- C-Level (Tier C — Industry Science): Zeta potential mechanisms; DLVO theory; ionic contamination effects; SSA-water demand relationships
Keyword：
Previous
More News
GOWAY INTERNATIONAL MATERIAL CO., LTD
Founded in 2009, we specialize in producing and supplying ,ceramic additives and related products, committing to supplying stable, environmentally friendly,professional and ceramic materials.
Contact UsContact Us
Company Phone/Wechat：86-0757-82131106 / +8613728575572
Company Fax：86-0757-82131106
Whatapp/skype: +8613600032377
E-mail：info6@goway-china.com
Office Address: Room C11-6, Foshan National Torch Innovation and Pioneer Park, Jihua 2nd Road, Chancheng District, Foshan City, Guangdong Province, China.
Factory Address: Nanbian Industrial Zone, Sanshui District, Foshan City Guangdong Province，China.