How to Prepare 5% – 10% Milk of Lime Slurry [Ca(OH)2] & Design Non-Clogging Recirculation Loops for Dosing Pumps

Table of contents

In industrial wastewater treatment plants, Hydrated Lime Ca(OH)₂ is the most economical alkaline reagent for acid neutralization and heavy-metal/fluoride precipitation, yet it frequently causes severe maintenance downtime due to jammed dosing pump check valves and rock-hard plugged uPVC pipelines. The root cause lies in its physical chemistry: the saturation solubility of Ca(OH)₂ at 20 °C is only 1.65 g/L (0.165%), meaning that in a 5%–10% w/w Milk of Lime slurry (51.8–107.2 g/L), over 98% of the lime exists as suspended solid particles. Eliminating pipe clogging requires combining ≥ 325 mesh (≤ 45 µm) grit-free Ca(OH)₂ powder with a continuous Turbulent Ring-Main Recirculation Loop operating at 1.2 – 1.8 m/s.

Moisture-proof 25kg chemical bag rack storage at Loc Thien Chemical warehouse

1. Retrograde Solubility of Ca(OH)₂ & Specific Gravity Table for 1% – 20% Milk of Lime

Because the dissolution of Calcium Hydroxide is mildly exothermic (ΔH = -16.7 kJ/mol), Ca(OH)₂ exhibits retrograde (inverse) solubility—dissolving less as water temperature rises (1.85 g/L at 0 °C, 1.65 g/L at 20 °C, 1.41 g/L at 40 °C, and 0.94 g/L at 80 °C).

Table 1: Specific Gravity, Baume, and Makeup Recipe for 1,000 Liters (1 m³) of Milk of Lime Slurry at 20 °C

Slurry Concentration (`% w/w Ca(OH)₂`)	Slurry Density at `20 °C` (`d`, kg/L)	Baume Degree (`°Be`)	Mass of `Ca(OH)₂` Powder per `1 m³` (`kg/m³`)	Volume of Clean Water per `1 m³` (`L/m³`)	Apparent Viscosity (`cP`)	Engineering Operating Recommendation
`1.0%`	`1.006`	`0.9 °Be`	`10.1 kg`	`995.9 L`	`1.2 cP`	Very dilute; requires large tank volume.
`3.0%`	`1.021`	`3.0 °Be`	`30.6 kg`	`990.4 L`	`2.1 cP`	Suitable for small WWTPs using diaphragm pumps.
`5.0%` (Optimal Standard)	`1.035`	`4.9 °Be`	`51.8 kg`	`983.2 L`	`4.5 cP`	Golden ratio for automated pH dosing; highly pumpable.
`8.0%`	`1.057`	`7.8 °Be`	`84.6 kg`	`972.4 L`	`12.0 cP`	Standard concentration for medium-to-large WWTPs.
`10.0%` (Upper Slurry Limit)	`1.072`	`9.7 °Be`	`107.2 kg`	`964.8 L`	`28.0 cP`	Maximum recommended concentration for piping loops.
`15.0%`	`1.111`	`14.5 °Be`	`166.7 kg`	`944.3 L`	`95.0 cP`	Non-Newtonian behavior begins; prone to settling in bends.
`20.0%`	`1.152`	`19.1 °Be`	`230.4 kg`	`921.6 L`	`280.0 cP`	Thick paste; restricted to Semi-Dry FGD atomizers.

2. Three Root Causes of Lime Dosing Pump & Pipeline Clogging

Flow Velocity Below Critical Settling Velocity (v ≤ 0.9 m/s) in Dead-End Lines: Suspended Ca(OH)₂ particles (solid density 2.24 g/cm³) require turbulent flow (Re ≥ 4,000, line velocity v ≥ 1.2–1.8 m/s) to stay suspended. In dead-end pipes fed by intermittent pulsing pumps, solids settle within 3–5 minutes whenever the pump pauses, packing 90° elbows solid.
Carbonation by Air Sparging (Ca(OH)₂ + CO₂ → CaCO₃↓): Using compressed air blowers to agitate lime tanks introduces atmospheric CO₂ that converts Ca(OH)₂ into hard Calcium Carbonate (CaCO₃) limestone scale on tank walls, pipes, and pH probes. Strictly use mechanical turbine agitators (1.5–2.5 kW/m³), never air sparging!
Coarse Unslaked Grit & Silica (SiO₂) in Low-Grade Lime: Crude lime containing > 5%–10% sand grit (> 150 µm) immediately jams ball check-valve seats and abrades pump rotors.

3. Non-Clogging Lime Slurry System Design Matrix

Table 2: Engineering Standards for Zero-Blockage Milk of Lime Dosing Systems

System Component	Common Faulty Practice (Causes Chronic Plugging)	Loc Thien Engineering Standard (100% Non-Clogging)
`Ca(OH)₂` Powder Specification	Crude lime (`Ca(OH)₂ ≤ 75%`, high sand grit).	Refined Industrial `Ca(OH)₂ ≥ 90%–96%`, fineness `≥ 325 mesh` (`≤ 45 µm`), insoluble grit `≤ 1.0%`.
Slurry Tank Agitation	Compressed air bubbling or undersized mixer without baffles.	Dual-impeller `45°` pitched-blade turbine (`120–200 rpm`, `1.5–2.5 kW/m³`) + 3–4 wall baffles + `1–2 mm` stainless top loading screen.
Slurry Transfer Pump	Small ball-valve diaphragm pump lifting from tank top.	Progressive Cavity (Mono) Pump, Peristaltic Hose Pump, or Open-Impeller Centrifugal / AODD Pump with flooded suction.
Piping Architecture	Dead-end line with sharp `90°` elbows; start/stop pump control.	Continuous Ring-Main Recirculation Loop running 24/7 back to tank top at `1.2 – 1.8 m/s` using long-radius bends (`R ≥ 5D`).
pH Dosing Modulation	Turning dosing pump motor ON/OFF directly.	Pneumatic Pinch Valve or Diaphragm Drop-Valve on a short vertical tee (`≤ 30 cm`) directly above the reaction tank.
Periodic Descaling	Waiting until pipe is blocked solid.	Automated `3–5 min` fresh water flush before shutdown; monthly `15 min` circulation with `2%–3%` dilute Hydrochloric Acid `HCl`.

Bulk tanker and truck delivery fleet of Loc Thien Chemical

4. Supply of 325-Mesh Refined Hydrated Lime Ca(OH)₂ by Loc Thien Chemical

Loc Thien Investment Development Co., Ltd. (LOC THIEN INVESTMENT DEVELOPMENT COMPANY LIMITED — Tax ID: 0313650856) is a specialized commercial supplier and distributor of industrial chemicals across Vietnam:

Refined Ca(OH)₂ Specifications: Active Ca(OH)₂ ≥ 90%–96%, ultra-fine air-classified ≥ 325 mesh (98% passing 45 µm), acid-insoluble residue ≤ 0.5%–1.0%, packed in moisture-proof 25 kg PE-lined PP bags or 500–1,000 kg Jumbo bags.
6 Strategic Warehouses (3,000+ tons/month, 5–30-ton fleet): Ba Ria - Vung Tau (Phu My 1 IP), Dong Nai (Long Thanh IP), Binh Duong (Di An City), Da Nang (Hoa Khanh IP), Can Tho (Tra Noc IP), and Bac Ninh (Tien Son IP). Legal Headquarters: 452/6B Tinh Lo 10, Binh Tri Dong Ward, Binh Tan District, Ho Chi Minh City.
Quotation & Delivery SLA: Technical quotation within 15 minutes; delivery within 4 hours in inner HCMC, 24–48 hours across Southern & Mekong Delta industrial zones, and 2–3 days in Northern & Central Vietnam. Contact hotline 0979 891 929 for detailed delivery procedures.

Product Pages: Industrial Hydrated Lime Ca(OH)₂ 96% | Poly Aluminium Chloride PAC 31% | Liquid Caustic Soda NaOH 32%–50%
GHS Safety Data Sheets (MSDS): MSDS Calcium Hydroxide Ca(OH)₂ | MSDS PAC 31%
Related Engineering Guide: Two-Stage Fluoride (F⁻) Wastewater Treatment Using Ca(OH)₂ and PAC
Technical Inquiry & 15-Minute Quotation: Hotline 0979 891 929 (tel:0979891929) — Email: [email protected].