Abstract: A porous absorbent made of a filter, a filter material or a sponge material is inserted into a polluted part of soil or groundwater containing environmental pollutants such as chlorinated solvents or heavy metal ions. The porous absorbent is inserted into the polluted environment such that its one end comes into contact with the pollutants and the other end is exposed to air. The porous absorbent allows the pollutants absorbed thereby to rise up to its air-exposed end through the vaporizing activity of the pollutant themselves and of the water containing them. The pollutants are allowed to evaporate from the air-exposed end to be dissipated into the air, or to concentrate at the air-exposed end for later removal. Further, microorganisms fixed to the porous absorbent are used to decompose pollutants for removal, or to absorb pollutants for removal. Those pollutant eliminating methods allow efficient elimination of even highly concentrated pollutants at a low cost without requiring complicated processes.

Abstract: A powder for a magnetic recording medium comprising a plurality of magnetic particles and a coating covering the surfaces of the magnetic particles. The coating is a residue resulting from the thermal decomposition of an organic material. The powder is manufactured by applying one or more organic materials to the surfaces of a plurality of magnetic particles by dispersing the magnetic particles in a solution containing the organic material. The magnetic particles, having the organic material as a coating, are separated from the solution, and the magnetic particles are heated to a temperature at which the organic material decomposes.

Abstract: Barium-ferrite series powders are prepared from an alkaline aqueous solution containing a prescribed ratio of ions of the metals equal to those contained in the powder. In the first stage, the alkaline aqueous solution is heated at a constant volume at 150.degree. to 300.degree. C. to precipitate a precursor of the barium-ferrite series powder. Then, the precursor is baked at 700.degree. to 1,000.degree. C. to crystallize the precursor.