In everyday life, people usually eat the walnut and throw away the shell. In industry, however, walnut shell is a valuable natural material used in water treatment, well plugging, agricultural products, and abrasive finishing. So, what makes it useful across so many different industries?
1. As a Filter Media for Water Treatment
Walnut shell filter media has hydrophilic and oleophobic properties, making it suitable for removing oil from wastewater, particularly streams with oil concentrations below 100 mg/L. It can also be cleaned and regenerated for reuse, making it a practical choice for oilfield wastewater treatment.
Test results indicate a dirt-holding capacity of 34.8 kg/m³ and a backwashing cycle of approximately 15 hours. With suitable cleaning agents and backwashing conditions, the oil content of filtered water can remain below 10 mg/L, while suspended solids can stay below 20 mg/L.
2. As a Material for Well Plugging
Reducing drilling-fluid losses depends partly on selecting suitable plugging materials and blending ratios. Research has shown that walnut shell powder combined with plugging agents and ultrafine calcium carbonate can help control minor fluid losses in wells.
It is used in plugging formulations to seal fractures and permeable formations, helping reduce fluid leakage and improve the effectiveness of drilling operations.
3. For Producing Nitrogen-Enriched Organic Materials
Under controlled temperature conditions and in the presence of an oxidizing agent, lignin can react with aqueous ammonia to produce ammoniated lignin for potential agricultural applications.
One process involves crushing and drying walnut shell, screening it through a 60-mesh sieve, and reacting it with aqueous ammonia, oxygen or hydrogen peroxide, and distilled water. The mixture is stirred and heated before the product is concentrated, dried, and tested for nitrogen content.
Research indicates that natural lignocellulosic materials can react with ammonia under these conditions. The final composition depends on the reaction process, so the product must be tested to confirm its suitability for agricultural use.
4. As a Raw Material for Activated Carbon and Other Industrial Products
Walnut shells can be processed into activated carbon and filter media for wastewater treatment in industries such as oil production, chemical processing, and leather manufacturing.
They are also used as natural tumbling and polishing abrasives for eyeglass components, jewelry, buttons, electronic parts, and stamped metal components. Their relatively gentle abrasive action helps remove minor burrs and improve surface finish without excessively damaging the workpiece.
In grinding wheel manufacturing, crushed walnut shell can serve as a pore-forming agent in vitrified grinding wheels. It helps create a porous structure that provides space for chips and supports grinding performance. Its convenient handling and relatively low cost make it useful in selected manufacturing processes.
In summary, walnut shell is more than an agricultural by-product. Its applications in filtration, drilling, agricultural materials, activated carbon, surface finishing, and grinding wheel production make it a versatile resource for industrial use.
