Advanced Treatment Technology for Stone Processing Wastewater

Stone processing wastewater is produced in large quantities during cutting, grinding and polishing. The wastewater contains a large amount of fine stone powder, cutting fluid, surfactant, tiny oil stains and inorganic additives.

It features high suspended solids, certain COD content, fine and difficult-to-settle particles. If treated only by simple natural sedimentation or single coagulation, the water body remains turbid, sludge compacts severely, and it is difficult to meet environmental discharge and production reuse standards.

1. Disadvantages of Traditional Treatment Processes

Most small and medium-sized stone factories traditionally adopt natural sedimentation or single PAC coagulation treatment, with obvious defects:

Fine stone powder particles carry negative charges and are stably suspended in water, settling slowly.
The natural settling speed is only 0.3–0.5 cm/min, occupying large pools and long cycle time.
After precipitation, the sludge is extremely dense and hardened, difficult to pump and clean.
The treated effluent is turbid, with high residual SS and COD, unable to recycle for long-term production.
Single flocculant dosing is unstable, with high consumption and high operating costs.

2. New Combined Process：Lime + Brine + PAM

This article adopts a composite process of lime conditioning + brine coagulation + PAM flocculation, aiming to break the stability of emulsified pollutants, accelerate particle agglomeration, improve settling efficiency, and optimize sludge characteristics.

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Add lime to adjust the wastewater pH to 10–11, destroy surfactant and cutting fluid emulsification, and precipitate organic oil stains.
Brine (magnesium salt) reacts in an alkaline environment to form fine magnesium hydroxide flocs, capturing ultra-fine stone powder particles.
Anionic PAM further aggregates small flocs into large dense clusters, realizing rapid sedimentation and clear water separation.

3. Experimental Data & Contrast Test

3.1 Basic Experimental Conditions

Raw water: On-site wastewater from stone cutting and polishing workshop
Experimental temperature: 25°C
Static settling time: 30 min
Core detection indicators: SS, COD, settling speed, sludge compactness, effluent clarity

3.2 Core Dosing Parameters (Optimal Scheme)

Lime dosing: Adjust pH stably between 10–11
Brine addition ratio: 0.15% of wastewater volume
PAM dosing concentration: 10 mg/L

3.3 Before & After Treatment Data Comparison

表格

Index	Raw Wastewater	After Treatment	Removal Rate
COD	78.2 mg/L	9.3 mg/L	Significant reduction
SS	40 mg/L	7.0–16.5 mg/L	Up to 82.5%

Original settling speed: 0.3–0.5 cm/min
Improved settling speed of new process: up to 60 cm/min

3.4 Sludge State Contrast

Traditional process: Sludge is dense, hardened, tightly stacked, difficult to pump and transport, high cleaning labor cost.
Lime + Brine + PAM process: Floc structure is loose and uniform, sludge will not harden, easy to pump, squeeze and subsequent filter press dewatering.

4. Comparison of Four Common Treatment Processes

4.1 Natural Sedimentation

Low cost, no chemical consumption;

Slow settling, large floor space, serious sludge hardening, poor effluent quality, not compliant for discharge.

4.2 Single PAC Coagulation

Simple operation;

Slow flocculation, poor removal effect on ultra-fine stone powder, turbid outlet water, high agent consumption.

4.3 Electrochemical Treatment

Good purification effect;

High equipment investment, high power consumption, complicated daily maintenance, not suitable for large-volume stone wastewater.

4.4 Lime + Brine + PAM Combined Process

Fast settling speed, short processing cycle
Stable removal of SS and COD, clear reuse water
Loose sludge, convenient subsequent dewatering by filter press
Low overall reagent cost and simple operation management
Strong adaptability for different stone processing wastewater

5. Practical Application Value

The treated effluent is clear and stable, which can be fully reused for cutting cooling water, realizing circulating water recycling and reducing fresh water consumption.
Loose sludge is more suitable for supporting filter press deep dewatering, the final sludge cake has low moisture content, low transportation and disposal costs.
The whole set of process occupies a small area, which is suitable for upgrading old sewage stations of small and medium stone factories and centralized treatment of stone industrial parks.
It can also be extended to mining wastewater, ceramic processing wastewater and other similar high-fine-suspension water quality treatment.

6. Conclusion

The combined process of lime + brine + PAM effectively solves the common problems of stone processing wastewater, such as difficult settling, hard sludge and substandard water quality.

With accurate experimental data and comparative verification, this scheme has the advantages of fast sedimentation, stable water quality, low operating cost and convenient sludge treatment.

Combined with filter press solid-liquid separation equipment, it can form a complete closed-loop treatment system, helping stone processing enterprises in Asia and Americas to achieve environmental compliance, water resource recycling and green production.

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