Membrane Filtration for Heavy Metal Removal

Membrane filtration for heavy metal removal exists in various types depending on the size of the particle that can be retained. The different types count microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). All types can be employed for heavy metal filtration of industrial wastewater. The different types of filtrations can be done by distinct membrane varieties made of different materials such as polymeric membranes and ceramic membranes.

The advantages of polymeric membranes are their dense pore size making this membrane type optimal and incredibly efficient for reverse osmosis filtration. However, polymeric membranes provide a low thermal and chemical strength level, making it challenging to handle aggressive fluids from harsh environments, which is often where heavy metal filtration appears to be necessary.

Whereas ceramic membranes made of silicon carbide are optimal and effective for membrane filtration for heavy metal removal because they are produced of inorganic material. As silicon carbide is the second hardest material in the world, only exceeded by diamonds, this material provides some excellent advantages. Contrary to polymeric membranes, silicon carbide ceramic membranes deliver mechanical, thermal, and chemical strength ideal for membrane filtration for heavy metal removal in harsh environments. Moreover, it means a longer membrane lifetime and a higher hydrophilicity level, which provides higher fluxes and fewer membrane fouling problems.

The feedwater enters the ceramic membranes to filter industrial water from, e.g., the mining industry, where heavy metals often appear in the wastewater. A feed pump triggers the filtration process by generating pressure, making the feedwater move through the membranes. The permeate will start to move through the membrane structure as a filtered liquid. Firstly, the permeate will move through the silicon carbide membrane layer. Secondly, the permeate will move through the membrane substrate structure, which is easier as this layer is made of larger silicon carbide gains than the membrane coating layer. The heavy metal filtration is completed, and the permeate will end up in a permeate tank without heavy metals and ready for further usage.

Another aspect of membrane filtration for heavy metal removal is the concentrate, which is concentrated feedwater. The concentrate is sent to subsequent processing en route to filtration. As this is concentrated feedwater, it is much dirtier than the actual feedwater. The permeate and the concentrate are now ready for further processing, reuse, or recycling. The permeate can be used as it is filtered. At the same time, the concentrate can be reused as it may contain essential unexploited resources, which can be valuable assets within other production processes.

Therefore, a membrane filtration system for heavy metal removal can be a tightly coupled system, where all parts play a significant role in water filtration. The feed pump initiates that the filtration occurs within the ceramic membranes.

As the wastewater is filtered, objects such as heavy metals, particles, oil, and other matter from the feedwater will eventually start to foul the membranes. Complete foul is avoided with a three-process cleaning procedure, which can occur either manually, semi-automatically, or automatically.

The first step of cleaning a membrane filtration system for heavy metal removal is a crossflow that cleans the membranes with feedwater due to the shear force on the membrane surface. This process is what happens most frequently.

The second process is a traditional backwash generated by a backwash pump, flushing water back through the membrane pores from the opposite direction.

The third process is a chemical cleaning-in-place, also referred to as CIP. Cleaning-in-place involves chemicals, heat, and water to clean the membranes without dismantling the water treatment unit. CIP is an effective method to clean the membranes quickly and efficiently, which is critical in liquid filtration processes such as heavy metal filtration. An effective cleaning process ensures low downtime of the whole membrane filtration system for heavy metal removal, which provides a more efficient and cost-effective operation. Dive into how a ceramic membrane is cleaned in this post.

The LiqTech membrane filtration for heavy metal removal utilizes the patented state-of-the-art ceramic membrane technology based on the inorganic material silicon carbide, also abbreviated SiC. Silicon carbide is the hardest man-made material and the second hardest material after diamonds globally. Utilizing this solid material secures a high-quality and robust membrane with a long working lifespan, even in severe environments. SiC is linked to unique advantages, such as providing a porous support structure, which only filtered water can permeate. In contrast, impurities such as heavy metals and other suspended solids are rejected. Besides that, SiC provides high flux, chemical resistance in all pH values from 0-14, and thermal resistance up to 800°C. Therefore, the membranes are ideal for heavy metal filtration.

In order to obtain all the desired effects of a ceramic membrane, a specific coating material is put on the walls of all flow channels of the membranes. This coating layer provides the membranes with ruggedness and durability and determines the membranes’ flow channel pore size and water flux.

Moreover, silicon carbide membranes provide:

• Highest flux for any membrane material
• Chemically inert
• Hydrophilic material (water-loving)
• Extremely hard and durable material 2930 +/- 80 kgf/mm3 (Vickers scale)
• Abrasive feeds
• Low power usage and low pressure
• Long membrane lifetime
• Low operational cost and low total cost of ownership

In addition, ceramic membranes also contribute to low energy consumption, capacity, and a small footprint to fight the global problem of clean water by enabling water reuse, recycling, and recovery.

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