At Hitachi Mill, two stage grinding circuit has been adopted since 1963, and a hydrocyclone is used for classifying the rod mill discharge.
The influences of some variables on the cyclone performance at high pulp densities in the feed pulp (5065% solids) were investigated based on the operating data.
The results obtained are summarized as follows.
(1) The separating size and the sharpness of separation were largely influenced by the feed pulp density.
(2) There was a half logarithmic relationship between the separating size and the solid recovery in the underflow.
(3) The sharpness of separation increased linearly with the solid recovery in the underflow.
(4) The sharpness of separation decreased with increased separating size and a half logarithmic relationship was obtained between them.
(5) It was pointed out that the fractional recovery curves should be drawn separately for the gangue minerals with low specific gravity and the sulphide minerals with high specific gravity, and so some more valuable informations could be obtained.

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Previous data on the water content W_f in the 2-phase froth and the authors' opinion for the fluidity of the solution contained among froth bubbles on the mere ground of bubble size and for the related minerals selecting ability of froths have been revised in this report.
Water content in frother solution froths under the specified aeration condition was determined by the froth suction method.
Froth decaying constant k₂ was caluculated from the height and W_f of the steady-state 2-phase froth.
The over-flow volume of the 2-phase froth was experimentally determined and from this result the froth fluidity constant k₃ was calculated. The W_f, k₂ and k₃, even if they are somewhat different in different experimental conditions, are considered by the authors to have some important bearing to the selecting ability of different frothers for the are flotation froths.

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This experiment was carried out for the purpose of elucidating the depression effect of sulfurous acid on the sulfide minerals in a flotation. The floatability of sulfide minerals were measured with varing the concentration of sulfurous acid by using Hallimond tube, and the critical curves of each mineral were determined.
And then, the depressant action of sulfurous acid was discussed through the calculation of the concentration of H₂S0₃, HSO₃-and SO₃-in solution.
The results obtained are as follows :
(1) The depressing effect of sulfurous acid on the sulfide minerals decreases in the following order Pyrite, Sphalerite, Galena, Chalcopyrite. The activated sphalerite is hardly depressed.
(2) The depressing effect of sulfurous acid and sodium sulfite on the sulfide minerals is almost the same.
(3) From the result of calculation of the H₂SO₃, HSO₃-, SO₃- concentrations along the critioal curves, it is recognized that the SO₃-concentration is nearly constant for Galena, Chalcopyrite and Pyrite.
The results are almost the same as in the case of sodium sulfite and it is considered that the depressant action of both reagents is mainly based on SO₃-concentration.

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In May 1966, Besshi-Niihama concentrator had adopted the pipe transportation of the pyrite concentrate (400 tpd) to Sumitomo Chemical Company Ltd., 2·4 Kilometers away instead of the former waggon transportation and now is achieving a smooth operation.
The pyrite concentrate is pumped by 50_??_ OH type Slime pump (reciprocating high pressure type) and 2·5 inches drawn steel pipeline.
The flow volume and pulp density are measured by an Electromagnetic flow meter and a γ-rays density meter respectively, and the dry weight of the transported concentrate is calculated by a multiplier with that data.

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廃津の有効利用の一環として, 昭和38年から, 廃滓および廃津たい積場上澄水 (鉱水) を用いて水稲の栽培試験を実施した.
栽培の総合成績は, 鉱水区-廃滓+土壌区-標準区-廃津区の順となった.この結果から, 大峰浮選廃滓はその土質特性 (透水性や塩基性など) の点から, 当地方の特徴である漏水田や老朽化 (酸性) 水田に対する土質改善用の客土として極めて適切であることが確あられた.さらに, 大峰廃滓たい積場の上澄水は, その水温が灌概用水に比らべて10℃以上も高いことおよびアルカリ性である (肥料の分解を促進する) ため, 水稲栽培に有効であった.このように, 大峰浮選廃滓は水稲栽培に良い影響を与えることがわかる.
昭和40年以後は, 一部農家において廃滓客土の適量試験および畑苗代での水稲苗育成試験を実施し, 生長の速い健苗の育成に成功している.そしてこの廃滓による客土化は次第に農家の関心をあつめてきている.
さらに岩手県農事試験場の果樹・疎菜園 (北上市) において, 大峰浮選廃滓を用いる強粘土質畑地土壌の改良試験も開始され, その有望性が認められてきている.

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