Technology Highlight: Non-Dissolving Suspended Solids in Leach Mining

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suspended solids in leach mining

As any operator of a heap-leach irrigation system knows, non-dissolving suspended solids in leach mining operations are a large contributor to irrigation system plugging, which leads to uneven solution distribution and thus decreased recoveries.  

What are Suspended Solids?  

“Suspended solids” refers to small solid particles that do not dissolve in water, thus remain in suspension as a colloid.  Colloids are used as one indicator of solution quality.  No two heap-leach operations will have identical solutions as the type and fraction of suspended solids will differ from operation to operation, but we can identify the usual suspects and their particle sizes:

ParticleClassSize
SandsFine0.06 – 0.2 mm
Medium0.2 – 0.6 mm
Course0.6 – 2.0 mm
SiltsFine0.002 – 0.006
Medium0.006 – 0.02
Course0.02 – 0.06
Carbon0.05 – 2.4mm
ClaysLess than 0.002
Challenges of Suspended Solids

When large quantities of suspended solids are present in solution, it is a matter of time before plugging becomes a problem. The small passageways of drip emitters and conical nozzles of sprinklers clog over time unless the suspended solids are removed from the system. At present the only solution for removal of these culprits are filtration systems, typically disc or screen manual filters, installed downstream from the pump station either in single units or larger assemblies based on solution flow requirements.  Filtration systems are a good starting point no matter what type of irrigation system is being utilized at your operation. However, with the harsh leach mining environment, experience has shown that filtering out suspended solids doesn’t always work out as intended. To filter out coarse to medium sands with a fine filtration element (mesh 30 – 70) is considered acceptable. But to filter out fine sands to coarse silts (mesh 70 – 625) filtration process is operationally inefficient. Any particle size smaller than coarse silts in practice is impossible to remove in a mining environment. Thus, we can deduct that a large percentage of suspended solids potentially in the solution cannot and will not be removed. To compound the problem, solution is being recycled through the leaching process in a closed cycle picking up more and more contaminants over time.  

Impact on Irrigation Systems

Having discussed the issues with filtration, let’s turn our attention on the impact of suspended solids on drip irrigation systems. The primary plugging point of a drip irrigation system are the drip emitters that control the flow rate of the overall system. There are two critical components of the drip emitter: Inlet Filtration Screens, and a Turbulent Flow Labyrinth Flowpath. Inlet filtration screens minimize the amount of suspended solids in solution entering the emitter, and the turbulent flow labyrinth decreases pressure and flow across the drip emitter to create the required drip action. Both of these components can be categorized as “passageways” through which the solution travels, and each passageway can be further quantified by their respective dimensions – width, depth, length, etc.

Now, having established that filtration of suspended solids is a rather difficult task and not always perfectly attained, we can deduct that the bigger the dimensions of so called passageways the less likely the suspended solids will be confined in a narrow zone and cause a build-up rendering the drip emitter plugged / clogged.  

Developing the Minoro Drip Emitter

During the R&D phase of the DRTS Minoro drip emitter by DRTS, a very thorough analysis was performed of the currently available drip emitter models produced by competing manufacturers. Our goal was to achieve a new level of product specifically for the mining industry, with which we could offer the same industry set drip emitter nominal flow rates, but most importantly stand out from the competition by increasing the dimensions of the critical components, something that today sets the Minoro far apart from the other manufacturers.  

Filtration Screens:

Flow rateOpeningsLength x WidthTotal AreaNote
1 LPH240.45 x 1.8mm19.4mm²35-45% more than competition*
2 LPH240.45 x 1.8mm20.5mm²40-60% more than competition*
4 LPH180.60 x 1.9mm20.5mm²40-60% more than competition*

Turbulent Flow Labyrinth Flowpath:

Flow rateWidth x DepthCross SectionNote
1 LPH0.75 x 1.22mm0.92mm²27-48% more than competition*
2 LPH0.90 x 1.40mm1.26mm²11-40% more than competition*
4 LPH1.40 x 1.60mm2.24mm²28-38% more than competition*

*(based on publicly available data and competitor product analysis)

In addition to having the largest dimensions of the two critical components to prevent drip emitter plugging, we also incorporate two unique features in the design of the Minoro drip emitter:

  1.  Elevated Filter Screens –  the large filtration screens have been placed at an elevated position from the inside diameter of the emitter to draw solution closer from the center of pipe – where velocity is higher and does not allow suspended solids to accumulate on the filter surface regardless of emitter orientation and during leaching off-cycles.  
minoro heap leach mining dripper

Minoro drip-emitter filter

  1. Patented Omniflow Turbulent Labyrinth – the Minoro Omniflow flow path eliminates non-turbulent “dead zones”, which are defined as areas of laminar flow where the velocity of solution is reduced considerably resulting in a lower flow. These points increase the chance of sedimentation, where suspended solids tend to accumulate and plug the emitter. The Omniflow flowpath is consistently turbulent from the inlet filter all the way to the outlet pool where the pipe is perforated and the solution exits the pipe. Below you can see an animation of water pressure increasing and decreasing in the Minoro Omniflow labyrinth versus a traditional labyrinth. Notice that Minoro has an unbroken chain of high velocity water flow due to the presence of “sharp teeth” along the entire length of the labyrinth which are not incorporated in other manufacturers’ emitter designs.

The combination of large filtration area, wide cross-sectional flowpath, and the elimination of “dead zones” are absolutely unique to the industry. The Minoro drip emitter by DRTS, was specifically designed for the leach-mining industry and is best in class based on larger critical component dimensions, making it less susceptible to plugging due to suspended solids.  If you would like to receive more information on this topic and our products/services please contact us.

 

2017 DRIP IRRIGATION TECHNOLOGY UPDATE