Treating wash water from coal preparation plants, recovering valuable coal fines, and maintaining closed-loop water circuits for sustainable, compliant operations.
Treat aggregate wash water for sand, gravel and quarry operations.
Tailings thickening and solids flux solutions for mining water recovery.
Groundwater treatment for open pit mining dewatering. Handle high suspended solids, metals and sulphates for discharge or reuse.
Acid mine drainage treatment systems for mining operations. Pyrite oxidation control, metal precipitation, pH neutralisation and safe sludge management.
Water Management in Coal Preparation
Coal preparation (washing) plants process run-of-mine (ROM) coal through crushing, screening, gravity separation (jigs and dense medium cyclones), and froth flotation to produce clean coal for power generation, steelmaking, and industrial use. Water is the primary medium for separating coal from mineral matter, with typical consumption rates of 0.5–2.0 m³ per tonne of clean coal produced. Effective water treatment is therefore integral to both operational efficiency and economic viability. Reynolds & Bauhm supply thickeners, flotation-tailings treatment and high-pressure filter presses that recover clean water for recycle and produce handleable fine-coal and reject cakes. Closing the water loop cuts make-up demand and meets the strict discharge limits placed on coal sites.
The key challenge in coal preparation water circuits is the handling of coal fines — particles below 0.5 mm with a low particle density of approximately 1.3–1.5 g/cm³. This low specific gravity makes gravity settling extremely slow, leading to persistent suspended solids in process water. In addition, clay slimes from associated shale and mudstone create stable colloidal suspensions that resist conventional clarification. Pyritic sulphur (FeS2) present in coal tailings poses a long-term acid rock drainage (ARD) risk if water is discharged to slimes dams without treatment.
Process chemicals further complicate water chemistry. Dense medium circuits consume magnetite (Fe3O4) as a separation medium, with losses to the water circuit requiring magnetic recovery. Flotation circuits use frothers and collectors that introduce surface-active compounds, increasing oil and COD loads. High dissolved solids from these reagents, combined with natural mineralisation, can elevate conductivity and TDS to levels that impair flotation selectivity if not controlled through water balance management.
Seasonal and operational variability adds further complexity. During wet weather, increased runoff can dilute process water and overwhelm settling ponds. During dry periods, elevated evaporation concentrates dissolved salts, potentially causing scaling in pumps and pipes. Startup and shutdown transients also disrupt water balance, requiring surge capacity in process water tanks to avoid overflow or shortages.
Reynolds & Bauhm provides integrated water treatment systems for coal preparation plants, combining mechanical separation, dissolved air flotation (DAF), high-rate thickening, and sludge dewatering to recover coal fines, recycle process water, and maintain closed-loop circuits with minimal freshwater make-up. Our designs account for the full range of operational variability, ensuring reliable performance under all plant conditions.
Typical Coal Prep Plant Water Characteristics
Coal preparation plant water quality varies significantly depending on the seam being washed, the proportion of fines, and the type of separation circuit. ROM coals with high clay content produce elevated slimes, while coals with high pyritic sulphur require particular attention to ARD risk in tailings. The table below summarises typical contaminant ranges and the treatment targets required for closed-loop reuse.
| Parameter | Typical Range | Treatment Target |
|---|---|---|
| TSS | 500–5,000 mg/l | <25 mg/l |
| Coal Fines | 200–2,000 mg/l | <10 mg/l |
| Clay Slimes | 100–1,000 mg/l | <5 mg/l |
| Pyritic Sulphur | 10–200 mg/l | <5 mg/l |
| Oil / Frother | 5–30 mg/l | <5 mg/l |
| pH | 5.5–8.5 | 6.5–8.5 |
| Magnetite | 10–100 mg/l | <5 mg/l |
| COD | 100–600 mg/l | <50 mg/l |
Integrated Coal Prep Water Circuit
Wedge wire screens or sieve bends remove coarse coal particles >0.5 mm from circuit water, protecting downstream pumps and separators from abrasion while pre-concentrating recoverable solids.
Magnetic drum separators recover dense medium magnetite (Fe3O4) from underflow streams. Recovery rates exceed 95%, reducing reagent costs and preventing magnetite accumulation in sludge.
Dissolved air flotation removes ultra-fine coal (<0.1 mm) and associated oil/frother residues. Coal-rich float is dewatered for product recovery; clarified water recycles to the plant.
High-rate thickeners or lamella clarifiers concentrate clay slimes and fine tailings. Overflow <25 mg/l TSS returns to the process water tank; underflow feeds dewatering.
Centrifuges or multi-disc screw presses dewater thickened tailings to 18–25% dry solids, minimising slimes dam volume. Recovered filtrate returns to the thickener feed.
A 1,000 tph prep plant typically loses 2–4% of ROM coal as fines to the water circuit. At a thermal coal scope of –90 per tonne, recovering 50% of these fines via DAF and centrifuge can generate –3.0 million in additional annual output — often exceeding the capital cost of the recovery plant within 12–18 months.
For coking coal operations, where fines command a premium scope of –180 per tonne, the economic case is even stronger. A 400 tph coking coal plant recovering 75% of <0.1 mm flotation fines can add –3.5 million to annual output, with project timelines as short as 6–10 months on the DAF and dewatering investment.
Specialised Equipment for Coal Prep Circuits
Dissolved air flotation is uniquely effective for ultra-fine coal (<0.1 mm) due to its low specific gravity. Micro-bubbles attach to hydrophobic coal particles, lifting them to the surface for skimming and dewatering, achieving >90% fines recovery.
Benefit: Recovers saleable product from waste stream
Screen bowl centrifuges combine filtration and centrifugal settling to dewater fine coal slurry from 25–30% feed solids to 18–22% cake moisture. Sieve bends provide low-cost pre-thickening ahead of centrifuges.
Benefit: Low moisture, saleable cake product
Deep-cone and high-rate thickeners with raked underflow discharge concentrate clay slimes from 2–5% to 25–35% solids. Flocculant dosing is optimised for fast-settling coal vs. slow-settling clay fractions.
Benefit: 70% smaller footprint than conventional
Cationic polyelectrolytes neutralise negative surface charges on fine coal and clay particles, promoting rapid agglomeration and settlement. Dose rates typically 5–20 g/tonne depending on slimes content.
Benefit: Rapid settling, clear overflow
Wet drum magnetic separators recover >95% of magnetite from DMC rinse water and drain screens. Efficient recovery maintains medium SG within ±0.01 of setpoint and prevents magnetite losses to tailings.
Benefit: Significant reagent operational benefits
Process water tanks with level control maintain circulating water volume during startup, shutdown, and upset conditions. Automated make-up water valves compensate for evaporation and product moisture losses.
Benefit: Minimal freshwater abstraction
Maintaining Water Balance in Coal Preparation
Make-up water = Evaporation + Moisture in clean coal product + Moisture in rejects + Irretrievable losses
For a modern closed-loop prep plant, total water losses typically amount to 5–8% of the circulating water load. This comprises evaporation from screens and sumps (2–3%), entrainment in product and reject streams (2–4%), and minor leakage or entrainment losses (<1%).
A 1,000 tonne-per-hour prep plant with a circulating water load of 100–150 m³ per tonne of feed will circulate approximately 3,500–5,000 m³/hr. At 5–8% losses, make-up water demand is 175–400 m³/hr. Implementation of thickener overflow recycle instead of slimes pond decant can reduce freshwater abstraction by 60–80%.
| Water Source | TSS (mg/l) | Suitability for Reuse |
|---|---|---|
| Thickener Overflow | 15–50 | Excellent — direct to process water tank |
| Slimes Pond Decant | 200–2,000 | Poor — requires re-treatment; high clay content |
| DAF Effluent | 10–30 | Excellent — low solids, minimal reagent residual |
An 800 tph thermal coal washery with 1,500 m³/hr of raw coal slurry and 1,200 m³/hr circulating clean water operates with a total circuit volume of 3,500 m³. Evaporative and entrainment losses total 80 m³/hr. By installing a high-rate thickener and DAF fines recovery unit, the plant reduces decant return from slimes ponds by 70%, cutting freshwater abstraction from 250 m³/hr to 80 m³/hr and saving an estimated per year in water requirements alone.
Reference Designs for Coal Preparation Water Treatment
Capacity: 1,000 tph ROM coal
Influent Characteristics: 3,500 m³/hr circulating water, TSS 800–2,500 mg/l, coal fines 300–1,200 mg/l, magnetite 20–60 mg/l.
Treatment Process: Sieve bend pre-screening → Wet drum magnetite recovery → DAF flotation (coal fines) → High-rate thickener (clay slimes) → Screen bowl centrifuge → Process water tank with automated level control.
Key Equipment: 2 × DAF-200 flotation units, 18 m ø high-rate thickener, 2 × screen bowl centrifuges, magnetic separator drum, 500 m³ process water tank, PLC/SCADA control panel.
Capacity: 400 tph ROM coal
Influent Characteristics: 1,200 m³/hr flotation circuit water, TSS 500–1,500 mg/l, ultra-fine coal <0.1 mm 150–600 mg/l, frother residual 10–25 mg/l.
Treatment Process: DAF unit with saturator → Lamella clarifier for overflow polishing → Screw press dewatering of combined float and underflow → Filtrate return to conditioning tank.
Key Equipment: 1 × DAF-100 unit, 120 m² lamella clarifier, 1 × multi-disc screw press, polyelectrolyte dosing station, 200 m³ filtrate tank.
Capacity: 600 tph ROM coal
Influent Characteristics: Existing slimes pond decant returning 120 m³/hr at TSS 500–1,800 mg/l; current freshwater make-up 180 m³/hr.
Treatment Process: Decant pumping station → High-rate thickener with cationic flocculant → Thickener overflow to new process water tank → Underflow to existing dewatering → Automated make-up valve and level control.
Key Equipment: 12 m ø high-rate thickener, 800 m³ process water tank, decant pump station (2 × duty/standby), automated make-up valve with flowmeter, SCADA integration to existing control room.
| Metric | Proposal 1 | Proposal 2 | Proposal 3 |
|---|---|---|---|
| Capacity | 1,000 tph | 400 tph | 600 tph |
Operational & Economic Advantages
Recover 50–70% of lost coal fines from circuit water, converting waste stream into saleable product –3 million annually for a large washery.
Thickener overflow and DAF effluent consistently achieve <25 mg/l TSS, suitable for direct reuse in dense medium and flotation circuits without impairment.
Closed-loop operation with thickener-based recycle cuts freshwater abstraction by 60–80%, reducing both water purchase costs and environmental licence risk.
Magnetic separation of dense medium losses maintains medium SG control and saves per year in magnetite reagent costs.
Minimising water discharge from coal tailings reduces pyritic sulphur oxidation and acid rock drainage liability, protecting long-term environmental compliance.
Fully closed-loop water circuits with no external discharge eliminate regulatory discharge limits and the need for costly effluent treatment ponds.
Explore Related Mining & Water Treatment Content
Browse our full range of mining water treatment solutions, including tailings management, process water, and site dewatering.
Mining & Minerals SolutionsTreatment systems for pyritic sulphur oxidation and acid rock drainage from coal and metal mine waste.
Explore Acid Mine DrainageHigh-rate thickeners and lamella clarifiers for solid-liquid separation in mining tailings applications.
Explore Tailings ThickeningDissolved air flotation units for fine particle removal, coal fines recovery, and oily wastewater treatment.
Explore DAF SystemsMulti-disc screw presses and centrifuges for efficient sludge dewatering operations, reducing disposal requirement and cost.
View Sludge ManagementDiscuss your specific requirements with our technical team and receive a tailored proposal for your project.
Contact UsAggregate & quarry water treatment systems for wash water, storm events, settlement ponds and recycled concrete aggregate.
View PageCoal mine wastewater treatment including acid mine drainage, tailings water and coal fines recovery.
View PageCopper mining water treatment for dissolved copper, molybdenum, flotation reagents, TSS and electro-winning bleed.
View PagePackaged, containerised, skid-mounted and research-station families engineered for sites with no road, no grid, no operator and no local supply chain.
All five product families plus the engineering choices that span the catalogue — transport envelopes, off-grid power, satellite SCADA, swap-on-failure spares.
Read the HubComplete plants delivered as a single pre-commissioned package — villages, mining camps, expedition bases.
Read More10′, 20′ and 40′ ISO container plants hardened for hurricane, arctic, desert and salt-air environments.
Read MoreModular skids sized to helicopter sling-loads, 4×4 trailers and ATV sleds for sites with no road access.
Read MoreContact our engineers for a tailored closed-loop water treatment and fines recovery solution.
Our expertise spans multiple industries with sector-specific water treatment solutions.