A method of rapid treatment of heavy metal sludge and preparation of ferrite magnets comprises following steps of: providing a sludge, the sludge at least having zinc metal and ferrous metal; adding an iron-containing substance to the sludge; pickling the sludge and the iron-containing substance with sulfuric acid to obtain a pickling solution with zinc ions and iron ions; neutralizing the pickling solution with sodium hydroxide to form hydroxide precipitates; and airing and heating the neutralized pickling solution by an ultrasonic-microwave method so that the hydroxide precipitates undergoing a ferrite magnet reaction, thereby obtaining ferrite magnets with a spathic structure.

A method of rapid treatment of heavy metal sludge and preparation of ferrite magnets comprises following steps of: providing a sludge, the sludge at least having zinc metal and ferrous metal; adding an iron-containing substance to the sludge; pickling the sludge and the iron-containing substance with sulfuric acid to obtain a pickling solution with zinc ions and iron ions; neutralizing the pickling solution with sodium hydroxide to form hydroxide precipitates; and airing and heating the neutralized pickling solution by an ultrasonic-microwave method so that the hydroxide precipitates undergoing a ferrite magnet reaction, thereby obtaining ferrite magnets with a spathic structure.

A grain-oriented M-type hexagonal ferrite has the formula MeFe.sub.12O.sub.19, and a dopant effective to provide planar magnetic anisotropy and magnetization in a c-plane, or a cone anisotropy, in the hexagonal crystallographic structure wherein Me is Sr.sup.+, Ba.sup.2+ or Pb.sup.2+, and wherein greater than 30%, preferably greater than 80%, of c-axes of the ferrite grains are aligned perpendicular to the c-plane.

A grain-oriented M-type hexagonal ferrite has the formula MeFe.sub.12O.sub.19, and a dopant effective to provide planar magnetic anisotropy and magnetization in a c-plane, or a cone anisotropy, in the hexagonal crystallographic structure wherein Me is Sr.sup.+, Ba.sup.2+ or Pb.sup.2+, and wherein greater than 30%, preferably greater than 80%, of c-axes of the ferrite grains are aligned perpendicular to the c-plane.

Provided are an anisotropic rare earth sintered magnet having a ThMn.sub.12-type crystal compound as a main phase and exhibits good magnetic characteristics, and a method for producing it. The anisotropic rare earth sintered magnet has a composition of a formula (R.sub.1-aZr.sub.a).sub.v(Fe.sub.1-bCo.sub.b).sub.100-v-w-x-y(M.sup.1.sub.1-cM.sup.2.sub.c).sub.wO.sub.xC.sub.y (where R is one or more kinds selected from rare earth elements and indispensably includes Sm, M.sup.1 is one or more kinds of elements selected from the group consisting of V, Cr, Mn, Ni, Cu, Zn, Ga, Al, and Si, M.sup.2 is one or more kinds of elements selected from the group consisting of Ti, Nb, Mo, Hf, Ta, and W, and v, w, x, y, a, b, and c each satisfy 7≤v≤15 at %, 4≤w≤20 at %, 0.2≤x≤4 at %, 0.2≤y≤2 at %, 0≤a≤0.2, 0≤b≤0.5, and 0≤c≤0.9), which contains a main phase of a ThMn.sub.12-type crystal compound in an amount of 80% by volume or more with the average crystal particle diameter of the main phase being 1 μm or more, which contains an R oxycarbide in the grain boundary area, and which has a density of 7.3 g/cm.sup.3 or more. The production method for the anisotropic rare earth sintered magnet includes grinding an alloy that contains a ThMn.sub.12-type crystal compound phase but does not contain an oxycarbide, then molding it in a mode of pressure powder molding with magnetic field application thereto to give a molded article, and thereafter sintering it at a temperature of 800° C. or higher and 1400° C. or lower to form an oxycarbide in the grain boundary area.

Provided are an anisotropic rare earth sintered magnet having a ThMn.sub.12-type crystal compound as a main phase and exhibits good magnetic characteristics, and a method for producing it. The anisotropic rare earth sintered magnet has a composition of a formula (R.sub.1-aZr.sub.a).sub.v(Fe.sub.1-bCo.sub.b).sub.100-v-w-x-y(M.sup.1.sub.1-cM.sup.2.sub.c).sub.wO.sub.xC.sub.y (where R is one or more kinds selected from rare earth elements and indispensably includes Sm, M.sup.1 is one or more kinds of elements selected from the group consisting of V, Cr, Mn, Ni, Cu, Zn, Ga, Al, and Si, M.sup.2 is one or more kinds of elements selected from the group consisting of Ti, Nb, Mo, Hf, Ta, and W, and v, w, x, y, a, b, and c each satisfy 7≤v≤15 at %, 4≤w≤20 at %, 0.2≤x≤4 at %, 0.2≤y≤2 at %, 0≤a≤0.2, 0≤b≤0.5, and 0≤c≤0.9), which contains a main phase of a ThMn.sub.12-type crystal compound in an amount of 80% by volume or more with the average crystal particle diameter of the main phase being 1 μm or more, which contains an R oxycarbide in the grain boundary area, and which has a density of 7.3 g/cm.sup.3 or more. The production method for the anisotropic rare earth sintered magnet includes grinding an alloy that contains a ThMn.sub.12-type crystal compound phase but does not contain an oxycarbide, then molding it in a mode of pressure powder molding with magnetic field application thereto to give a molded article, and thereafter sintering it at a temperature of 800° C. or higher and 1400° C. or lower to form an oxycarbide in the grain boundary area.

A ferrite sintered magnet comprises a plurality of main phase grains containing a ferrite having a hexagonal structure, wherein at least some of the main phase grains are core-shell structure grains each having a core and a shell covering the core; and wherein the minimum value of the content of La in the core is [La]c atom %; the minimum value of the content of Co in the core is [Co]c atom %; the maximum value of the content of La in the shell is [La]s atom %; the maximum value of the content of Co in the shell is [Co]s atom %; [La]c+[Co]c is 3.08 atom % or more and 4.44 atom % or less; and [La]s+[Co]s is 7.60 atom % or more and 9.89 atom % or less.

A ferrite sintered magnet comprises a plurality of main phase grains containing a ferrite having a hexagonal structure, wherein at least some of the main phase grains are core-shell structure grains each having a core and a shell covering the core; and wherein the minimum value of the content of La in the core is [La]c atom %; the minimum value of the content of Co in the core is [Co]c atom %; the maximum value of the content of La in the shell is [La]s atom %; the maximum value of the content of Co in the shell is [Co]s atom %; [La]c+[Co]c is 3.08 atom % or more and 4.44 atom % or less; and [La]s+[Co]s is 7.60 atom % or more and 9.89 atom % or less.

The present invention provides a ferrite sintered magnet comprising ferrite crystal grains having a hexagonal structure, wherein the ferrite sintered magnet comprises metallic elements at an atomic ratio represented by formula (1). In formula (1), R is at least one element selected from the group consisting of Bi and rare-earth elements, and R comprises at least La. In formula (1), w, x, z and m satisfy formulae (2) to (5). The above-mentioned ferrite sintered magnet further has a coefficient of variation of a size of the crystal grains in a section parallel to a c axis of less than 45%.
Ca.sub.1-w-xR.sub.wSr.sub.xFe.sub.zCo.sub.m  (1)
0.360≤w≤0.420  (2)
0.110≤x≤0.173  (3)
8.51≤z≤9.71  (4)
0.208≤m≤0.269  (5)

The present invention provides a ferrite sintered magnet comprising ferrite crystal grains having a hexagonal structure, wherein the ferrite sintered magnet comprises metallic elements at an atomic ratio represented by formula (1). In formula (1), R is at least one element selected from the group consisting of Bi and rare-earth elements, and R comprises at least La. In formula (1), w, x, z and m satisfy formulae (2) to (5). The above-mentioned ferrite sintered magnet further has a coefficient of variation of a size of the crystal grains in a section parallel to a c axis of less than 45%.
Ca.sub.1-w-xR.sub.wSr.sub.xFe.sub.zCo.sub.m  (1)
0.360≤w≤0.420  (2)
0.110≤x≤0.173  (3)
8.51≤z≤9.71  (4)
0.208≤m≤0.269  (5)