Accurate Slurry and Pulp Level Measurement

This is a guest post by Bill Hancock, President of Zeroday Enterprises

Accurate Slurry and Pulp Level Measurement

Accurate Slurry and Pulp Level Measurement when there is a froth or foam on top of the flotation cell, mixing tank or sump can be challenging under many conditions. Reasons for pulp level monitoring and measurement include:

  1. Mechanical measuring devices such as float balls and ultrasonic targets can become covered with solids causing the device to hang up, become heavy and sit in the slurry deeper and/or the slide mechanism gets jammed and stuck preventing smooth operation.
  2. Slurry density (% solids) fluctuations cause float-ultrasonic and pressure differential devises to vary. Changing slurry apparent specific gravity will cause the float ball to ride higher or lower in the slurry even if the slurry level stays constant. Pressure differential devices, such as bubble tubes and pressure differential electronic sensors, measure based on slurry weight above the device so will provide proportional pulp level readings as slurry densities change.
  3. Basic froth mechanics, particularly in flotation cells, where bottom layers of the froth bed will be quite wet because fine bubbles coursing upward to the froth will push entrained slurry into the froth. As the fine bubbles coalesce into larger bubbles and rise to the top of the froth bed, this slurry drains back into the cell. When froth characteristics or operating conditions change, the amount of water and slurry in the bottom layers of the froth will vary and make proper froth-slurry interface depth measurement more problematic.

Point #3 is worth dwelling on because this is often overlooked or not well understood. A rough representation of a mineral flotation froth cross section is provided below. The fine bubbles generated by the flotation cell impeller rise to the bottom of the froth bed and coalesce into larger bubbles as these rise in the froth. The values are upgraded as the bubbles coalesce because the bubble surface area decreases with the result being less particle carrying capacity. Probabilistically the weakest, least hydrophobic particles are released and drain back into the cell.

slurry and pulpThere is a massive amount of air in a flotation cell, typically 12-25% of a float cell’s total volume, which rises enmass to the froth layer as fine bubbles. Much slurry is pushed into the lower froth bed which is held in the voids between the bubbles until the slurry can drain back into the cell. As illustrated in the figure, there is more slurry in the lower froth bed than higher due to drainage.

This slurry in the void spaces between the bubbles must and will drain to the float cell. However there will be some slurry holdup before draining which can make the pulp-froth interface indistinct and difficult to define depending on the amount of slurry held in the froth. The amount of slurry carried into the froth can significantly vary.

Mechanical and pressure differential slurry level measuring techniques can have difficulties consistently and precisely monitoring the pulp-froth interface level under these conditions. However, electrical conductance pulp level measurement techniques can more effectively and consistently define the froth-pulp level interface height.

The conductive LTM pulp level monitoring probe technology dramatically reduces the complication of slurry level interface monitoring under a wide range of froth and flotation conditions. Because the probe is quite sensitive and measures at very low conductance levels, the probe capably and consistently measures at very low slurry (e.g. water) concentrations.

It is possible to define the slurry-froth interface level as the precise point where there is distinctly very low conductance due to a lack of slurry, at the depth where there is a predominance of air. In essence this is an electrical circuit on-off signal where the LTM pulp level monitoring probe identifies the depth where the froth is sufficiently drained preventing electrical current transmittance. From a logical reasoning standpoint this is a practical and effective measure. And is the slurry level interface level the LTM probe monitors.

Bill Hancock is an internationally recognized expert in mineral processing technologies, technical marketing management and water treatment. Hancock founded and owns Zeroday Enterprises which supplies chemical mix-feed systems, LTM conductive slurry level monitoring probes, peristaltic hose and tube pumps, mixers and flocculant and coagulant chemicals. He also founded Argo Consulting—a technical and technical marketing consulting practice focused on providing mineral processing, water treatment and technical marketing consulting services to the mining industry.

Flocculants: How Do They Work and Why?

This is a guest post by Bill Hancock, President of Zeroday Enterprises

How Do Flocculants Work and Why?

Have you ever wondered how flocculants work at the colloid (small particle) level?

Flocculants enhance, and are often required to make possible solid-liquid separations from turbid to high percent solids in water.  Typically, solid particle sizes in water have a wide normal distribution and are inorganic and organic based.   If these particles are denser than water, the particles will settle to the bottom of a container if given sufficient time; however, many of the smaller, lighter particles remain suspended (think a cloudy mud puddle that appears to swirl with activity) for a much longer time than allowed with a typical residence time.  That is because the particles, or colloids, are small enough to remain suspended by external forces including Brownian motion (interaction with the water molecules), thermal currents, dispersive surface charges and the like.  These are the hardest particles to treat because they are so fine and do not easily and quickly settle.

How do Flocculants work and why?

Unless the particles are uniformly coarse (depending on the water chemistry conditions and relative solid and water densities, coarse particles might be considered greater than 100 mesh or greater than 210 microns) and rapidly settle by gravity, flocculants are required to aggregate multiple particles together as ‘floccules’ which are pseudo-large particles.  Enter the flocculants!

Polymers are ubiquitous materials ranging from nylon, polyethylene plastics, Teflon, and starches to amino acids.  Flocculants belong to the water soluble polymer class, and so they fully dissolve in water.  These are acrylamide based with functionality groups which allow the polymers to readily chemically adsorb to particles.  These polymers are very long (for perspective, if you expanded a flocculant molecule to 1 inch in diameter, the total length would be on the order of 1.25 miles long!)  As flocculant molecules dissolve in water, these molecular chains (ropes) are free to uncoil and expand, but are never completely linear due to random Brownian motion and water thermal current effects.

In effect, these flocculant ropes lasso aggregates of particles together.  Since the polymer chains are very long, these polymers agglomerate multiple colloidal and coarse particles together.  As these flocculated aggregates continue to mix, the polymer rope continues pulling the particle aggregate into a tighter and denser floccule, which causes the particles to settle more readily. The larger floccules are more easily filtered, centrifuged and floated in a dissolved air flotation unit.

A simple visual demonstration of this process is represented in the accompanying animation video.  The animation shows the initial step of ‘coagulation’ where a short cationic (positive) charged polymer coagulant is added to partially neutralize the repulsive particle negative charges and induces pin flocc aggregation of the colloidal particles.  Then the flocculant molecules ‘lasso’ and flocculate these pin floccs into larger floccules.

Bill Hancock is an internationally recognized expert in mineral processing technologies, technical marketing management and water treatment. Hancock founded and owns Zeroday Enterprises which supplies chemical mix-feed systems, LTM conductive slurry level monitoring probes, peristaltic hose and tube pumps, mixers and flocculant and coagulant chemicals. He also founded Argo Consulting—a technical and technical marketing consulting practice focused on providing mineral processing, water treatment and technical marketing consulting services to the mining industry.

Number One in Safety the Past Five Years

safetyNumber One in Safety the Past Five Years

At Mainland Machinery Ltd, Health & Safety is our top priority. We are fully compliant with all the latest safety certification requirements, and ensure alignment with our client’s HSE systems and end goals. Realizing that one of the largest objectives of clients is a clean safety record, we have worked strenuously to improve and realize a top-notch program that satisfies our clients and ourselves. The dedication and perseverance of our team has ensured exemplary safety standards. Whether it’s in our shop or in the field, we get the job done safely.

Unparalleled COR Scores

Each year our HSE System is independently audited for legislative compliance. We are proud to report that our 2016 COR Audit resulted in a score of 100%! Our Safe Companies COR scores are also unparalleled for the past five years, maintaining a yearly average of 100%. As we have proven ourselves in the matter of HSE, clients continue to look to us to bring a standard of safety that is unmatched.

Innovative and Ongoing HSE Auditing, Training and Operations

  • COR Certified
  • CWB Approved
  • CSA Standard W47.1 Certified
  • ISNet World Registered
  • Avetta (formerly PICS Auditing) Registered
  • ComplyWorks Registered
  • Continuous HSE training and updates

Exceeding HSE Program Expectations

At Mainland, we are not just satisfied with meeting the minimum HSE standards. In fact, we have achieved the best injury rate in our classification unit for the past five years! Mainland is a world class company producing a world class outcome in all that we do.

Whether you are retro-fitting your feed mill, producing equipment for the oilfield, installing mining equipment or in forestry operations, Mainland has the safety record, qualifications and experience to get your job done right.

Could Deep-Sea Mining Be Canada’s Next Gold Rush?

deep sea miningCould Deep-Sea Mining Be Canada’s Next Gold Rush?

Traditionally, mining has been a prolific source of income for Canada and other countries throughout the world. With land-based deposits becoming increasingly scarce, mining companies have had to seek out other sources that could be mined, including ocean floors. Vastly covering two-thirds of the Earth’s surface, oceans have been largely unexplored until now. However, the ocean floors are known to possess abundant mineral resources.

This is exciting news for the mining industry in Canada. With the longest coastline in the world and access to three different oceans, Canada has great potential for deep-sea mining resources. So much that we need to ask, will deep-sea mining be Canada’s next gold rush?

The Ocean is a Rich Source of Minerals

The ocean floor is covered in aqueous vents, which are geothermal fissures that cut deeply into the earth’s crust. These vents spew minerals from deep inside the Earth into the ocean that settle in rock deposits known as massive seafloor sulfides. 

Massive seafloor sulfides consist of coveted rare earth metals, including copper and platinum. These deposits are of high quality because they are newer than dry-land deposits and have not had a chance to degrade or disperse. Many of the dwindling copper deposits on dry land feature copper with a 0.6 grade, while deep-sea copper deposits have been shown to be as high as 7.2.

Deep-Sea Mining Methods Differ from Traditional Methods

Deep-sea mineral deposits cannot be extracted through traditional mining methods. Many of these deposits are found at depths that make manual extraction impossible. Moreover, because these mineral deposits are located underwater, most established mining methods would not apply.

In order to bring these minerals to the ocean’s surface, mining companies are developing remotely operated robots to do the work for them. These robots are connected to ships floating above the mineral deposits that are used to operate the machines and collect the minerals that are extracted. Much of this technology is still in the early stages of development, but it appears to show promise.

Worries of Possible Environmental Impact

Many critics have warned of the potential environmental impacts of deep-sea mining. Little is known about the complex ecosystems located on the seafloor and scientists worry that deep-sea mining operations could cause irreversible damage.

Proponents of deep-sea mining argue that it could actually be more environmentally friendly than surface mining. Surface mining has had a significant negative impact on the environment by causing polluted waterways, devastated habitats and displaced communities.

Deep-sea mining does not require companies to drill into the Earth’s surface. As a result, it does not produce the same waste that surface mining does and there is less disruption to surrounding ecosystems. Additionally, human communities are not displaced, as the mineral deposits are not located in habitable areas.

What Deep-Sea Mining Means for Canada

Canadian companies are leading the charge in developing deep-sea mining technology. Toronto-based Nautilus Minerals is the first company in the world to be granted a deep-sea mining lease in 2014. This 20-year lease is located 30 kilometers off the coast of Papua New Guinea on a site known as Solwara 1. Nautilus plans to start operations within the next five years.

Though other deep-sea projects are in development in Europe, Nautilus Minerals’ Solwara 1 operation is set to become the first active deep-sea mining site in the world. With Canadian companies on the cutting edge of deep-sea mining, Canada is poised to be a leader in this exciting new industry. 

Reclaiming Oil Sands

oil sand reclamationReclaiming Oil Sands

Canada’s oil sands have always been controversial. Despite their economic benefits, critics are concerned over the environmental damage the oil sands cause. Alberta’s oil sands are surrounded by pristine wilderness, and development has caused what is considered irreversible damage.

However, a number of Canadian companies are working to return the area to its natural state. With companies such as Syncrude pumping up to $60 million a year into researching land reclamation techniques, Canadian oil field companies are on the cutting edge of oil sands restoration efforts.

The Challenges of Land Reclamation

Alberta’s oil sands are located under an area covered by dense Boreal forest and wetlands. In order to extract the petroleum from the ground, large swaths of forest must be cleared to make way for open pit mines, or steam must be pumped into wells to separate bitumen from the soil. The waste water generated by these processes is stored in highly toxic “tailing ponds,” which account for about 25 per cent of the area disturbed by oil sands development. These ponds are one of the largest problems for environmentalists.

To be certified as reclaimed, any traces of man-made impact must be removed, and the land must be capable of generating native plant and animal life. This makes reclaiming wetlands complex, due to the diverse mix of life contained therein.

Can a Forest Be Rebuilt?

A number of companies operating in the oil sands region are doing their part to ensure that disturbed areas are restored to their native Boreal forest.

Collaboration between industry heavyweights such as Shell Canada, Suncor Energy, Nexen Energy and Husky Energy has resulted in 2.5 million trees and shrubs being planted. The project has replanted about 700 hectares of land disturbed by industrial development.

Replanting these areas rather than allowing them to regrow on their own ensures that the areas are not overtaken by invasive plant species and that animal habitats are not disrupted.

Cutting-edge Techniques

Completely restoring the wetlands disturbed by oil sands development is the greatest challenge of land reclamation. Syncrude’s Sandhill Fen research project, however, is making strides.

The purpose of the project is to create a sustainable wetland environment and share successful techniques with other companies and organizations. This has resulted in a 50 hectare, man-made pollution-free watershed built from tailing sands. Although no animals have been reintroduced to the area – as it is still part of an active mine site – some animals have begun to return on their own.

Other projects, such as Suncor Energy’s Nikatonee Fen, have achieved similar success.

Cleaning up Tailing Ponds

The removal of tailing ponds is another key priority in restoration efforts. The most important development in this aspect of cleanup has been Suncor’s centrifuge plant. The centrifuge returns the water from tailing ponds to its natural state by spinning it rapidly to remove the solid pollutants. The plant became operational in early 2015 and is expected to reduce tailing ponds by 50 per cent.