The histrical review of producing aluminium since 1825 is outlined. Yearly production rates surpass other metals. In 1970, over 10, 000, 000 tons of aluminium was produced. The resources of bauxite are estimated to be over 5, 000, 000 tons.
Recently the technics for alumina production are directed for mechanization and automatic control. The plant capacity is increasinh, the largest one has 1, 500, 000 tons alumina per year. In the field of electrolysis, the anode type generally adapteg was changed from prebaked multiple to Söderberg continuous horizontal and to vertical. But recently large current 100-150kA pot preboked anode type system has been favored again. Mechnizations of operation was largely adopted. In the large current pot, the effect of magnetic field becomes serious and the bus arrangement for compensation is explained.
The aluminium industry will develop constantly and in the year 2000 the world praduction will reach 50, 000, 000-90, 000, 000 tons.

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Barite nodules have been collected at the Sin Guri Bank in the Japan Sea by a survey ship of the Hydrographic Office of Japan. The Sin Guri Bank is situated at about 30km southwest of the Oga peninsula, and the rocks consist of Miocene yellowish siltstone, diatomaceous mudstone, two pyroxene andesite and trachybasalt. Barite nodules, occurring with diatomaceous mudstone, were collected in latitude 39°38.4'N, longitude 139°31.3'E and at a depth of 152m. Those barite nodules have well-rounded shapes being 1-20cm. in diameter and are widely distributed in the Sin Guri Bank. Diatom contained in diatomaceous mudstone is correlated to the basal part of the Funakawa formation and the upper part of the Onnagawa formation of the Middle Miocene.
In the present study, two specimens, ellipsoidal and orbiculate, weighing 362g and 142g respectively as shown in Photo. 1, were used. Barite nodules are compact and homogeneous, but have mudstone-like texture. Their individual mineral particles are not ob, served megascopically. A microscopic observation reveals that a large amount of diatom and radiolaria are contained in barite aggregates consisting of about 0.02-0.1mm particles, and a few other minerals. Specific gravity of the nodules is 3.59-3.74 (by a Berman balance) and X-ray diffraction patterns are in good agreement with that of typical synthetic barium sulphate and no other mineral is detected. DTA curve does not show any characteristic thermal reaction, and after heating at 1, 000°, no change in X-ray diffraction pattern was observed compaing with the unheated materials. The result of chemical analyses indicates 73.08-84.84% BaSO₄ and a small amount of SrSO₄, PbSO₄, and CaSO₄.
The content of BaSO₄ in this barite nodules is almost the same as that already reported barite nodules off Colombo, Indian Ocean, and off the San Clement Island, California.
The present authors consider the genesis of this barite nodules as follows: The SO₄ ion in the diatomaceous mudstone reacted with the ascending Ba-bearing hydrothermal solution resulting in the precipitation of barite.

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In order to make clear the mechanism of the improved reaction between xanthate ion and sulphide mineral due to the dissolved oxygen, the change of the electronic state at the mineral surface was examined.
The capacitance on the surface of the single crystal of galena and sphalerite was measured to investigate the variation of the flat band potentials by the adsorption of oxygen.
The flat band potentials of both galena and shalerite are more noble in a solution containing dissolved oxygen than in a solution free from oxygen.
From the results, it is considered that the adsorption of oxygen on mineral surface causes the change in the electronic surface state of the mineral and forms the surface state in which positive charges on the mineral surface are increased relatively according to the acceptance of electrons by oxygen.

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While the Kynch's the ory serves as a usefull means to elucidate the behavior of settling particles, its applicability is limited by the anomalous behavior of practical suspensions such as in colliery waste water, while the same may be said in regard to the application of the Coe-Clevenger formula.
These formulae were derived with the factors limited to the settling curve of mud line with no consideration to the measured concentration gradient in sedimentation zone.
By conventional methods, however, it was very difficult to measure the concentration gradient, hence, the authors attempted to solve this problem by use of γ-ray density meter.
Using this method, measurements could be made continuously without disturbing the settling system.
This report describes the accuracy of density measurement and the results of the change of vertical density distribution against time under several conditions using a few samples such as colliery waste water etc.
Namely, accurate measurements within the value of ±0.002g/cm³ were obtained and the density of suspensions over wide range were determined. The density destribution in a vertical direction in a settling tube was not always continuously changed. The concentration gradient in the presence of added flocculants was discussed.

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Some experiments on the recovery of nickel from laterite ore by the ammonia pressure leaching have been carried out in the current investigation. Hydrogen was used as the reducing gas, and ammonia solution containing ammonium sulphate was used as the leaching solution for the recovery of nickel from the reduced ores. The experimental results obtained are summarized as follows;
(1) It is required for the efficient extraction of nickel that laterite ores are reduced with H₂ gas at the rate beyond the critical flow rate during the reducing roasting, because the amounts of nickel oxides contained in laterite ores are very small.
(2) The leaching rate of nickel by the ammonia pressure leaching is about sixteen times greater than that by of the atmospheric ammonia leaching.
(3) The ammonia solution containing ammonium sulphate is more effective than that containing ammonium carbonate to obtain the leached solution without ferric ions.
(4) The extraction of nickel exceeds 90 percent when the experiment on the recovery of nickel from laterite ore was carried out under the following reduction and extraction conditions: reduction temnerature 900°C, the flow rate of H₂ gas 200cc/min, reduction time 90 min, leaching temperature100°C, oxygen pressure 2kg/cm², stirring rate 500rpm and the concentration of ammonia and ammonium sulphate 3mol/l and 1mol/l, respectively.
(5) More satisfactory pretreatment of laterite ore for the pressure leaching is attained by the reduction with H₂ gas than by that with CO gas, which was descrided in our previous paper, because the extraction of nickel by the ammonia pressure leaching is not affected by the metallic iron formed during the reducing roasting.

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