Thickener Underflow Density Measurement

Thickener underflow density describes the concentration of the slurry leaving the lower discharge of a thickener. A continuous reading can show how that stream changes between water, normal slurry and denser operating conditions.

The useful question is not simply “what is the density?” It is which decision the signal will support: underflow pumping, recirculation, downstream filtration, mass-flow calculation or process investigation. The required location, response and validation plan follow from that decision.

• Normal, minimum and maximum slurry density
• Solids type, particle behaviour and liquid phase
• Pipe diameter, material, wall thickness and orientation
• Pump type, pulsation and water-flush periods
• Expected air, settling, scaling and abrasion
• Sampling point and laboratory reference method
• Required outputs, alarms and control-system use

At Grupo Mexico, Rhosonics reports an SDM ECO installed at a tailings-thickener underflow to provide real-time readings and work with a flow meter for mass-flow calculations. The published installation used a clamp-in arrangement on an existing 8-inch pipe.

Rhosonics also reports a South African thickener-underflow comparison against an existing nucleonic meter. That case is relevant evidence for the tested process, not a blanket performance promise for another ore, pipe or calibration.

Density does not by itself identify particle-size distribution, mineralogy, viscosity, bed level, flow rate or the cause of a process change. Combine the trend with pump state, flow, valve position, pressure, sampling and downstream performance.

Entrained air, a partially full pipe, settling and composition changes must be considered during selection and commissioning. Pause the project if the site cannot identify a representative measurement and reference point.

1. Define the control or monitoring decision. Record who will use the signal and what action follows.
2. Survey the line. Confirm dimensions, material, orientation, pressure, flow condition, access and isolation.
3. Characterise the slurry. Capture normal and upset ranges, solids and liquid composition, temperature, air and abrasion.
4. Select the integration. Review the current manufacturer options against the actual mechanical duty.
5. Plan validation before installation. Agree sample timing, laboratory method, operating points and acceptance tolerances.
6. Commission with context. Store the density trend alongside the process signals needed to interpret it.

Continue with the SDM ECO installation and commissioning guide or view the SDM ECO product page.

Where is a density meter installed on a thickener?

For underflow measurement it is normally reviewed on the discharge line, but the exact location depends on pipe fill, pumps, bends, recirculation, sampling and access. Do not choose a position from a generic drawing alone.

Can density be used to calculate mass flow?

Density can contribute to a mass-flow calculation when combined with a suitable volumetric-flow measurement, aligned units and measurements representing the same stream.

Can an ultrasonic meter replace a nuclear gauge?

It may be a candidate, but replacement suitability must be demonstrated for the specific slurry, location and operating range. Use the technology comparison and replacement checklist.

Reviewed 10 September 2026 against the Grupo Mexico SDM ECO case, the manufacturer’s thickener-underflow comparison, the current SDM ECO product information and operating manual. Results belong to the cited installations; site-specific engineering and acceptance evidence remain necessary.

Send PMA the slurry range, solids and liquid details, pipework, pump arrangement, flow conditions, proposed sampling method and the decision the density signal must support.