Purifying agent for purifying soil or ground water, process for producing the same, and method for purifying soil or ground water using the same

A purifying agent for purifying soil or ground water, comprising a water suspension containing:

• iron composite particles comprising α-Fe and magnetite, and having an average particle diameter of 0.05 to 0.50 μm, an S content of 3500 to 10000 ppm and an Al content of 0.10 to 1.50% by weight;
• and
• polyaspartic acid or a salt thereof;
• and
• wherein said iron composite particles contained in the purifying agent are present in an amount of 10 to 30% by weight based on the weight of the purifying agent, and said polyaspartic acid or salt thereof is present in an amount of 5 to 50% by weight based on the weight of the iron composite particles.