Miike Colliery has a total of 3 pits, called Yotsuyama, Miyaura and Mikawa respectively, and Mikawa pit is the most important one of Miike Colliery.
Coal dust explosion occurred at No.1 Mikawa-Incline of Miike Colliery, on November 9, 1963.
At that time, the output of the colliery was some 400, 000 tons a month. The number of persons employed in this colliery was 8, 650. No.1 Mikawa-Incline was about 2, 000m long with 12° of dip, and it had the sectional area of 25m². The quantity of intake air of this incline was 4, 000m³ a minute. The belt conveyor with 12 steps was arranged on the right, side and the winding track on the left side. The track was used for winding of only materials and deberis every day except holidays and of men on holidays.
When the train of 10 debris tubs was beeing wound, the link between the 2nd and the 3rd tubs was broken and 8 tubs escaped. The escaped train of 8 tubs was derailed at 310mL point, then brought down the rail arches and crashed into the frame of the belt conveyor. Consequently the coal dust cloud turned up and the explosion occurred. It was 3. 12 p.m. just the time of relief between 1st and 2nd shifts.
In this explosion, 1, 290 persons were killed or injured. But out of 458 persons killed, only 20 persons were killed by the shock of explosion and others were poisoned to death with CO gas grown after the explosion.
Testings of links and coal dusts were carried out in several research institutes. But we could not decide whether the breaking of the link had been due to the bad material or the fatigue of it. There were 2 opinions whether the coal dust cloud was grown from the settling coal dust on rail arches etc. or from the raw coal on the conveyor belt.
Coal dust cloud was surely ignited by the frictional heat among the escaped tubs, rails and frame of belt conveyor, or by the electric spark of the cable destroyed with escaped tubs. As these positions were very near, we could not decide which had been the real course of ignition. The position of the original ignition was suspected to be between 310mL point and No.11 BC engine room.

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The disaster of coal dust explosion that occurred at No.1 inclined shaft of Mikawa Pit Miike Coal Mine on November 9, 1963 is considered to have been resulted from a runaway occident of the mine tubs due to the break of its link.
At that time, the authors who hod been entrusted with the task of judging the cause for this disaster carried out detailed investigations on the quality of the broken link, its mechanical properties, especially the existence of fatigue and the load of fracture.
In this paper the results from those investigations are reported.

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The nondestructive analytical method of silicon and aluminium, components of ash in coal, has been studied by application. of fast neutron reactions of 14Mev neutron, produced by the midget type neutron generator tube. The available neutron flux of the generator is about 1.2×10⁵n/cm²/sec for 14Mev neutron and 1×10⁴n/cm²/sec for thermal neutron.
The sample coal and two standard samples (pure aluminium and silicon) were irradiated close together in irradiation hole of moderator for 10min., each standard sample consists of 0.5g of aluminium or siliconpowder dispersed in 5g of benzoicacid. By this irradiation; appreciable amounts of²⁸Al and ²⁷Mg have been produced due to the reactions as²⁸Si (n.p) ²⁸Al, ²⁷Al (n.γ) ²⁸Al and ²⁷Al (n.p) ²⁷Mg. Then, gamma activities of samples have been measured with 100-channels Nal scintillation spectrometer.
The silicon and aluminium content in a given sample coal can be determined by the comparing the photo peak counts of ²⁸Al and ²⁷Mg of a given gamma ray from the sample coal with the photo peak counts of these nuclides from same gamma ray in the spectrum of the standard sample. The relation between them are caluculated by the following eqations:
C_A=C_SAχ+C_AAY
C_M=C_SMχ+C_AMY
where, C_A and C_M are net counts of ²⁸Al and ²⁷Mg photo peak of an irradiated coal sample, respectively. C_SA and C_SM are net counts of ²⁸Al and ²⁷Mg photo peak of unit weight of irradiated silicon, respectively.
C_AA and C_AM are net counts of Al and Mg photo peak of unit weight of irradiated aluminium, respectively.
The content of silicon and aluminium in the sample coal determined by this proposed method agreed close with the results given by original chemical analysis. According the experiment, analytical limit of sensitivity of this method can be evaluated as 4mg for silicon and 12mg for aluminium in net weight for a given sample under the following consideration: relative standard deviation of net counts of ²⁸Al and ²⁷Mg photo peak≤20%.

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Various fundamental experiments were carried out on the influence of coal dust upon spark discharge, and, the experiments were performed under conditions as similar as possible to those in coal mines. The results-obtained were as follows:
(1) When coal dust is dropped on the electrode in a glass vessel, corona current increases and spark voltage decreases. The smaller the sizes of coal particles are, and the larger the quantity of the dropped coal dust is, the greater the effect will be.
(2) When DC voltage is impressed at the needle to plate electrode, the effect of polarity is remarkable, and this is considered to have certain bearings with the attached quantity of coal dust.
(3) When compared with other dusts, coal dust is observed to be particularly influential on spark discharge.
(4) On the influence upon surface discharge, of accumulated coal dust placed on the insulating plate: coal, dust in small quantity makes electric current increase and makes the break-down, voltage along the plate surface decrease, but as the quantity of coal dust increases, the current decreases, and the voltage increases.
(5) On the relation between the accumulated quantity of coal dust and the breake-down voltage along the plate surface: the break-down voltage shows the maximum value at a certain point of accumulated quantity of coal dust, and when the quantity is over that point, the voltage becomes decreased.

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The effect of sodium sulphide on the prevention of copper activation for sphalerite was studied.
The adsorption of copper ion on sphalerite was measured in the solution containing copper ion and sodium sulphide with varying a pH value of solution. From the results, it is recognized that the adsorption of copper ion is prevented completely in an alkalin solution containing sodium sulphide. While, the adsorption of copper ion not prevented by raising the pH value of solution.
In the case where sodium cyanide is used-as a depressant, the effect of sodium sulphide on the prevention of copper activation was investigated. Until a certain amount of sodium cyanide, the floatability of sphalerite increases with the increase of sodium cyanide. It is confirmed that this phenomenon causes by the coating of copper sulphide particles precipitated by sodium sulphide on the sphalerite surface. However, increasing the concentration of sodium cyanide to over 30mg/l, depressing effect of sodium cyanide becomes distinguished by the addition of sndium sulphide.
In the case where sulphurous acid is used as a depressant, the floatability of sphalerite does not decrease at the low pH value and the colloidal sulphur is formed by the decomposition of sodium sulphide. However, with the increase of the pH value and the amounts of sulphurous acid, the depressing effect of sulphurous acid becomes vigorous in the presence of sodium sulphide.
Consequently, it may be considered that the copper activation for sphalerite is prevented perfectly by using sodium sulphide.

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The removal of silica dissolved in sodium aluminate solution is one of the serious problems in production of highly purified alumina. The solution used here was prepared by leaching the laterite ore roasted with Na₂CO₃. Among various addition agents so far used for, removal of silica, it was found that the dolomite gave the best results and about 99% of silica was removed as a result of heat treatment of the solution in autoclave at 170°C, thus resulted in less than 0.03 as a value of SiO₂×100/Al₂O₃ in the solution. The products formed by addition of dolomite powder contained calcium silicate hydrate, calcium aluminum hydroxide and basic aluminum silicate besides excess dolomite.

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