Recover process water from tailings streams and achieve high underflow densities with optimised thickening technology, polymer selection, and solids flux engineering.
Treat aggregate wash water for sand, gravel and quarry operations.
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.
Dewatering water treatment for pits, tunnels and underground mines.
Global Tailings Production & Water Scarcity
The mining industry generates approximately 14 billion tonnes of tailings every year worldwide. These tailings streams typically carry 15-35% solids by weight, with the balance being process water that represents both an operational cost and a valuable resource. In arid regions and jurisdictions with strict water licensing, the economic and regulatory pressure to recover and recycle this water has never been greater. Reynolds & Bauhm design high-rate and paste thickeners with flocculant dosing that lift underflow density and return clarified water to the plant. Recovering this water cuts make-up demand, shrinks the tailings footprint and supports safer, drier tailings storage.
The choice of thickening technology fundamentally shapes a mine's water balance, energy consumption, and tailings management strategy. While conventional thickeners remain appropriate for low-risk applications with ample water supply and generous TSF capacity, modern operations facing water scarcity, limited disposal space, or stringent closure obligations are increasingly specifying high-density and paste thickening systems. These advanced technologies achieve underflow concentrations that were previously unattainable without mechanical dewatering, effectively blurring the boundary between thickening and filtration.
Conventional thickening technology, developed in the mid-20th century, was designed primarily for general solid-liquid separation with underflow densities of 40-50% solids. Modern mining operations increasingly demand higher underflow concentrations to reduce Tailings Storage Facility (TSF) volumes, improve water balances, and enable alternative disposal methods such as dry stacking. This has driven the evolution from conventional thickeners through high-rate, high-density, and ultimately paste and deep cone thickeners capable of producing underflows exceeding 75% solids.
The Global Industry Standard on Tailings Management (GISTM), published in 2020, establishes rigorous requirements for tailings facility design, operation, and closure. A core principle is minimising TSF footprints through reduced water content and improved engineering. High-density and paste thickening directly support this objective by delivering significantly denser underflows, reducing TSF volume requirements by 30-50% compared with conventional deposition.
Water balance modelling for closed-loop circuits demonstrates that even modest improvements in thickener underflow density translate to substantial reductions in make-up water requirements. A copper concentrator processing 5,000 m³/day at 20% feed solids can reduce make-up water from over 2,000 m³/day with conventional thickening to under 650 m³/day with high-density thickening at 68% underflow. These figures drive the technical case for thickener upgrades and greenfield paste plant investments across the sector.
Selecting the Right Technology for Your Application
| Thickener Type | Feed % Solids | Underflow % Solids | Rise Rate | Typical Application |
|---|---|---|---|---|
| Conventional | 15-25% | 40-50% | 0.5-1.5 m/h | General tailings, pre-thickening |
| High-Rate | 15-25% | 50-60% | 2-5 m/h | CIP/CIL circuits, high capacity |
| High-Density | 20-30% | 65-72% | 1-3 m/h | Dry stacking, reduced TSF volume |
| Paste | 25-35% | 72-78% | 0.5-1.5 m/h | Surface disposal, underground backfill |
| Deep Cone | 30-40% | 75-85% | 0.2-0.8 m/h | Extreme dewatering, filtered tailings |
Rise rate indicates the settling velocity of the suspension; higher rates permit smaller vessel diameters for equivalent throughput.
Thickener selection depends on more than target underflow density. Feed particle size distribution, solids specific gravity, settling characteristics, and rheological behaviour all influence equipment sizing and geometry. High-rate thickeners rely on feedwell optimisation and flocculant addition to achieve rapid settling, while paste and deep cone units require steep floor angles (typically 30-60 degrees) and high-torque rake mechanisms to convey dense underflow to the discharge point.
Climate and site elevation also affect design. At high altitudes, lower atmospheric pressure reduces dissolved air availability for auxiliary flotation stages. In cold climates, viscosity increases can retard settling and require heated process water or insulated vessels. Reynolds & Bauhm is involved in designing account for these variables through site-specific pilot testing and CFD modelling of feedwell hydrodynamics.
Engineering Fundamentals for Thickener Sizing
The flux density function describes the rate at which solids settle through a suspension as a function of concentration. It is defined as:
G(φ) = φ × v(φ)
Where G(φ) is the solids flux density (t/m²/h), φ is the volumetric solids concentration, and v(φ) is the hindered settling velocity. As concentration increases, the settling velocity decreases non-linearly due to particle-particle interaction.
For a given feed concentration, there exists a critical flux above which the thickener will fail to achieve the desired underflow density. The limiting flux is the minimum value of the total flux curve and represents the maximum solids throughput per unit area that the thickener can handle. Exceeding this rate causes solids to accumulate in the clarification zone, leading to overflow turbidity and underflow dilution.
Engineers determine the limiting flux through batch settling tests (Coe-Clevenger or Talmage-Fitch methods) or continuous pilot trials. The flux curve is constructed from settling velocity measurements at varying solids concentrations, enabling graphical or numerical identification of the limiting condition.
Reynolds & Bauhm provides pilot-scale thickener testing with diameters from 0.5 to 2.0 metres, enabling direct measurement of flux behaviour with site-specific tailings and candidate polymers under representative process conditions.
The required thickener surface area is determined by dividing the solids mass flow rate by the limiting flux:
A = Qfeed × Cfeed / Glimit
Where A is the unit area (m²), Qfeed is the volumetric feed rate (m³/h), Cfeed is the feed solids concentration (t/m³), and Glimit is the limiting solids flux (t/m²/h).
A gold operation processes 1,000 tonnes per day of tailings solids at a feed concentration of 25% solids by weight. The target underflow is 65% solids. Batch settling tests indicate a limiting flux of 0.49 t/m²/h at the compression point.
Feed solids mass flow = 1,000 tpd ÷ 24 h = 41.67 t/h
Required unit area = 41.67 t/h ÷ 0.49 t/m²/h = 85 m²
This corresponds to a thickener diameter of approximately 10.4 metres. Adding a 15% safety factor for operational variability and feed fluctuations, a 12-metre diameter high-density thickener would be specified.
High-density and paste thickeners operate with deep compression beds (2-5 metres) that exert significant torque on the rake mechanism. Drive selection must accommodate not only normal operating torque but also upset conditions such as bogging or slump events. Modern designs incorporate torque-limiting clutches, bed level sensors, and variable-speed drives to protect mechanical components while maintaining consistent underflow density.
Matching Flocculant Chemistry to Tailings Composition
Flocculant performance is dictated by surface chemistry, not generic solids concentration. A polymer optimised for iron oxide tailings will fail catastrophically on bentonite slurries. Our laboratory programme tests candidate products across charge type, molecular weight, and dosage on representative tailings samples to identify the lowest total cost of ownership.
High-molecular-weight anionic polyacrylamide is the workhorse flocculant for clay-rich tailings including kaolinite, bentonite, and smectite-dominated streams. The negative charge density complements the cationic edge charges of clay platelets, promoting strong inter-particle bridging.
Dosage: 20-60 g/t solids
Preferred for sulphide tailings such as pyrite, chalcopyrite, and sphalerite where the mineral surface carries a net negative charge at typical process pH. Cationic polymers adsorb strongly via electrostatic attraction, forming dense, fast-settling flocs even at low dosages.
Dosage: 15-40 g/t solids
Effective for siliceous ores such as quartz and feldspar where surface charge is near-neutral. Non-ionic polymers rely on hydrogen bonding and van der Waals forces rather than electrostatic attraction, making them tolerant of water chemistry variations.
Dosage: 25-70 g/t solids
Branched polymer architectures create larger, more permeable floc structures with higher settling rates but lower mechanical strength. Linear polymers produce compact, shear-resistant flocs ideal for applications with intense mixing or pumping. Selection depends on the shear environment downstream of the flocculation stage.
Higher molecular weight polymers (>18 million Da) generate larger floc sizes and faster settling rates but require gentler mixing to avoid chain scission. Lower molecular weight products form smaller, tougher flocs suitable for high-shear thickeners or pressure filtration. The optimal MW balances floc size, settling velocity, and shear stability.
High ionic strength process water (common in recycled circuits) can compress the electrical double layer, reducing polymer effectiveness. High charge density polymers maintain performance in saline environments, while low charge density products may require increased dosage. Jar testing with site water is essential for confident selection.
Quantifying Recovery and Make-Up Requirements
The fraction of feed water recovered to the overflow stream is calculated from mass balance:
Recovery = (Quf × (1 - Cuf)) / (Qf × (1 - Cf))
Where Quf and Qf are underflow and feed volumetric flow rates, and Cuf and Cf are the corresponding solids concentrations by volume.
Make-up water is the difference between process water demand and recovered water. For a perfectly closed circuit with no evaporative or entrainment losses:
Make-up = Qf × (1 - Cf) - Quf × (1 - Cuf)
In practice, make-up must also account for evaporation from the TSF, moisture retained in shipped concentrate, and entrainment in filter cakes. Typical mining operations experience 5-15% additional water loss beyond the thickener balance.
A concentrator receives 5,000 m³/day of tailings feed at 20% solids by weight. The high-density thickener produces underflow at 68% solids.
Feed water = 5,000 × (1 - 0.20) = 4,000 m³/day
Solids mass = 5,000 × 0.20 × 2.7 t/m³ = 2,700 t/day (assuming solids SG 2.7)
Underflow volume = 2,700 t/day ÷ (0.68 × 2.7 + 0.32 × 1.0) = 1,473 m³/day
Underflow water = 1,473 × 0.32 = 471 m³/day
Water recovery = (4,000 - 471) / 4,000 = 87%
Make-up water required = 471 m³/day (plus evaporation losses)
By comparison, conventional thickening to 45% solids would yield only 64% water recovery, requiring 1,440 m³/day make-up. The high-density thickener saves approximately 970 m³/day of freshwater abstraction.
A 2% decrease in underflow density from 68% to 66% increases make-up water by approximately 110 m³/day. Conversely, improving underflow to 70% reduces make-up by a further 95 m³/day. These sensitivities underscore the economic value of precise thickener control and real-time density monitoring via nuclear density gauges or ultrasonic bed-level sensors.
Reference Project Feasibility
Scope includes structural steel tank, dual-deck feedwell, auto-dilution system, and PLC-based rake torque and bed level control. Expected underflow density 58% solids at design throughput. Polymer station sized for 50 g/t anionic PAM with dual dosing pumps and day tank.
Deep cone geometry with 55-degree floor angle and 2.5 MNm rake torque rating. Positive displacement piston pumps deliver paste at 200 kPa to surface disposal area. Includes cyanide destruct monitoring interface, underflow density loop control, and emergency overflow containment.
High-density thickener with centre-pier drive and 4.0 MNm torque rating. Ceramic disc filters achieve 18% moisture cake for dry stacking. Package includes filter feed pumps, vacuum system, cake conveyor, and dust suppression. Filtrate returns to process water tank.
Operational & Environmental Advantages
Investing in modern thickening technology delivers returns across operational, environmental, and regulatory dimensions. The benefits compound over the mine life through reduced water requirements, deferred TSF capital, and lower closure liability.
Return the majority of process water to the mill circuit, reducing freshwater abstraction and associated pumping costs by up to 70% compared with unthickened discharge.
Higher underflow densities directly reduce Tailings Storage Facility capacity requirements by 30-50%, extending facility life and deferring costly expansion or new dam construction.
Smaller volumes of underflow slurry reduce downstream pumping energy and pipeline wear. Energy benefits 25-40% are typical when upgrading from conventional to high-density thickening.
Paste and deep cone underflows enable filtered and dry-stacked tailings, eliminating conventional dam risks and supporting progressive rehabilitation and closure.
Mineral-specific flocculant selection reduces chemical consumption by 15-30% versus generic programs, with corresponding reductions in logistics and handling costs.
Meet the Global Industry Standard on Tailings Management through reduced water content, improved geotechnical stability, and lower long-term environmental liability.
Explore Connected Solutions
Our mining water treatment capabilities extend from thickening and clarification to filtration, dewatering, and site remediation. Explore these related technologies and services.
Broad overview of water treatment solutions for mining operations including tailings, process water, and site dewatering.
Mining & Minerals SolutionsTreatment of acidic, metal-laden mine water with neutralisation, precipitation, and solids separation systems.
Explore Acid Mine DrainageWater quality management for flotation circuits including reagent compatibility and recycled water effects.
Explore Mining Flotation WaterHigh-rate inclined plate clarification for pre-thickening and process water treatment with 70% smaller footprint.
View Lamella ClarifierMulti-disc screw presses and centrifuges for tailings and sludge dewatering to minimise disposal requirements.
View Sludge ManagementSite-specific batch and continuous trials to validate thickener sizing, polymer selection, and underflow density targets before full-scale commitment.
Learn About Pilot TestingAggregate & quarry water treatment systems for wash water, storm events, settlement ponds and recycled concrete aggregate.
View PageCoal preparation plant water treatment: coal fines recovery, closed-loop water systems, pyritic sulphur removal, DAF flotation.
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 PageTailings ponds and process-water dams require aeration to manage sediment oxygen demand and prevent H₂S liberation.
Contact our process engineers for thickener sizing, polymer selection, and water balance modelling. We offer site-specific pilot testing, CFD simulation of feedwell hydrodynamics, and Capital expenditure-Operating expenditure optimisation studies to support your investment decision.
Our expertise spans multiple industries with sector-specific water treatment solutions.