Effervescent compositions, for remediation of aqueous solutions, containing zero-valent iron particles, easy to manufacture, cost-effective and highly active in remediation of pollutants, especially of heavy metals and organic compounds. NZVI tablets are innovative and environmentally-friendly. They act extremely fast, exhibiting high remediation ability in just few minutes. The tablets are stable to store and occupy small storage space, could be used in various remediation aspects, especially under urgent and demanding conditions, and when a fast and high activity is needed.