| Ocean manganese nodules (OMN) is an important ocean mineral resource with great future strategy and the traits of large reserves, wide-ranging distribution. In industry, OMN can be applied to extract metals in wet metallurgy with the Reductive Ammonia Leaching method, but the large amount of reduction-ammoniacal leaching residue (RALR) generated in the process limit its larger-scale application. In this study, an important manganese oxide-cryptomelane was synthesized using OMN and RALR as raw materials.OMN minerals were firstly sintered with some inorganic potassium salts by calcining reaction separately, cryptomelane wasn't observed in the sintering product. However the product calcining with OMN and K2MnO7 after pickled by the acid revealed an excellent capacity of adsorbing K. The mechanism may be with the porous tunnel of OMN and the defect of the crystal structure by pickling out K+in the product.The nanocrystalline cryptomelane was synthesized with RALR minerals by hydrothermal method using potassium persulfate as the oxidant. It is shown that the optimal range of pH value for the preparation is between 5 and 7. Meanwhile, in the reaction system potassium ions function as the dynamic template and sulfate ions stimulate the synthesis of nanocrystalline cryptomelane. The prepared cryptomelane product is possessed of large specific surface area, good crystallinity and excellent capabilities of oxidation degradation to methylene blue because of the redox reaction of Mn(IV). The product also exhibited excellent catalysis for the decomposition of methylene blue dye with H2O2. When H2O2 was adsorbed to the surface activity of cryptomelane, it produced large amounts of 3 kinds of free radicals(OH·, HOO·and O2·) by chain reaction which can quickly oxidation organic.In summary, the synthesis of cryptomelane in the study can reduce its preparation cost and facilitates its industrialized application. Moreover, it provides a new approach for the recovery and utilization of the RALR of OMN.
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