When purchasing iron sludge (often a byproduct of water treatment or metal processing), the most critical factor is the Total Iron Content (Fe), which typically ranges from 40% to 70% depending on the source. You must also verify the Moisture Content, as high water levels significantly increase shipping costs and affect processing efficiency; ideally, it should be below 10-15% after dehydration. Additionally, check the Particle Size Distribution to ensure compatibility with your recycling or smelting equipment.