In Japan, almost no natural gypsum is mind for industrial uses, and almost all gypsum is synthetic gypsum, that isdesulpho-gypsum, produced by waste sulfur dioxide gas from metal smelters, power plants and other industrial waste sources. The amount of such synthetic gypsum production has reached more than six million metric tons per year in 1979. Major uses are for cement and building material. Other uses are for soil conditioner, investment casting mold, organic composite materials, etc. and sulfur recovery by gypsum decomposition is being examined. This paper summarizes present Japanese stajs and new application of synthetic gypsum produced from desulphowaste gas.

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Thermal decomposition of two dolomite-like double carbonate minerals was investigated by means of DTA and X-ray technique.
One was magnesian kutnahorite (Ca_1.064 (Mn_0.475, Mg_0.437, Fe_0.024)(CO₃) ₂) from the Ryujima mine, Nagano Prefecture, the other was ferromanganoan dolomite (Ca_1.115 (Mg_0.415, Fe_0.225, Mn_0.245)(CO₃) ₂) from the Budo mine, Niigata Prefecture, Japan.
DTA measurements were performed in the three atmospheric conditions, 1) in static air, 2) in CO₂ 100ml/min gas flow, 3) in CO₂ 95ml/min+CO 5ml/min mixing gas flow. Their DTA curves measured in static air atmosphere using minute sample masses were quite different from those published previously. These differences might be due to the effect of self-generated atmosphere (CO₂).
In the CO₂ gas flow at 100ml/min, the magnesian kutnahorite was decomposed in four steps, while the ferromanganoan dolomite in three steps as follows. Magnesian kutnahorite
→CaCO₃+Mgz MnO4+Mn304+MgO→CaCO₃+CaMnO₃+Mgo→CaCO₃+CaMnO₃+Ca₂MnO₄+MgO→CaMnO₃+Ca₂MnO₄+MgO+CaO.
Ferromanganoan dolomite
→CaCO₃+ (Fe, Mn) ₃O₄+MgO→CaCO₃+CaMnO₃+CaFe₂O₄+MgO→CaMnO₃+CaFe₂O₄+MgO+CaO.
However, in the flowing gas mixture of CO₂ 95ml/min+CO5ml/min, both samples showed two-step decomposition like dolomite according to the following processes. Magnesian kutnahorite
→CaCO₃+M, Mn) O→ (Ca, Mn) O+ (Mg, Mn) O. Ferromanganoan dolomite→CaCO₃+ (Mg, Mn) O+Fe₂O₃→Ca₃MgFe₃O₆+ (Ca, Mn) O+ (Mg, Mn) O.
Consequently, it was found that a dolomite-like double carbonate could be decomposed in the two-step reaction, only when it was heated in the CO₂ atmosphere having sufficiently low O2 partial pressure.

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Fracture conductivity measurements in the laboratory are made under confining pressures up to 30MPa atambient temperature, using water as flowing fluid. Three kinds of proppant, i. e. glass beads, Goshiki silica sand (Japan) and Ottawa silica sand (Canada), and two kinds of rock, i. e. Berea sandstone (U. S. A.) and lnada granite (Japan) are put to the test.Simulated packed fractures are prepared by placing a proppant between core halves. Decreases in fracturethickness and porosity with pressure are calculated by an amount of water squeezed out from the fracture with an increasein confining pressure. Change of specific surface of the proppant with an increase in confining pressure is calculatedby fracture conductivity, fracture thickness and porosity. The confining pressure at which proppant crushing or proppant embedmentinto walls of fracture occurs is estimated from the change of the specific surface.

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It has been already proved that intrinsically safe circuit voltages can be used from 2 V to 800 V for explosive gas atmosphere, but these values have no relation to electric shock accidents.
On account of the reason intrinsically safe circuit voltages in coal mines have been controlled less than about 25 V to prevent electric shock accidents customarily.
In case of a fault voltage occured at a part of circuit, however, if the product of the touch voltage and its touch time exists within a certain range, the incidence of electric shock accident will be very low.
In this paper the author describes an experimental study of the allowable voltage in intrinsically safe circuit which is based on a small touch time which don't lead to the impediment in a human body under usual circumstances.
Synthesizing the experimental results of each paragraph of this paper, the conclusion is as follows;
(1) In case of a circuit containing the bare electrode is stalled at a soaked point, usable voltage is under AC 25 V or DC 60 V.
(2) In case of a circuit containing the bare electrode is stalled at a point usual dried or a circuit not containing the bare electrode, usable voltage is under AC 100 V or DC 200 V.
As for over voltages above mentioned, if the intrinsically safe construction is kept in drip-proof increased safety construction, it will be usable to AC and DC 800 V.

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The supersonic fire jet burner is now using not only for piercing of rocks, but for treatment of many kinds of industrial wastes or grinding of rocks into very fine particles. But the burner has a pretty high heat loss-about 25 to 27 % of total heat generated in combustion chamber, for it was developed as a jet piercing machine which requires small diameter of combustion chamber. Length - Diameter ratio of combustion chamber in the jet piercing machine was usually 10 to 15, and the amount of heat transferred across a surface of chamber was pretty large. Using of jet burner in grinding of rocks or treatment of wastes permits us to change the construction parameters, which decrease the heat loss of burner. The Length Diameter ratio of combustion chamber of new developed high efficiency jet burner was reduced to about 3.0, and it has the heat loss less than 10 %. The authors developed also a special superheated vapour burner, temperature of which would be changed voluntary but contained the supersonic velocity of jet and high pressure. This type of burner is useful for drying or grinding of organic material or combustibles. The paper reports the construction of new developed burners and some results of experiments which carried out to determine the optimum parameters.

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In order to find the critical speed of a rotating rod surrounded with no casings in an off-shore boring, the naturalcircul ar-frequency of lateral vibration of a vertical pipe in water, the both ends of which were fixed, or the lower end ofwhich w as fixed and the upper end of which was simply supported, has been studied theoretically when the pipe was subjected to an axial thrust, its own weight, a twisting moment and a fluid force. Furthermore, the above results have been checked by experiments.
The results obtained are as follows:
1) The critical speed of rod decreases with the increase of either one of the thrust, own weight and twisting momentif th e other conditions are same. As the twisting moment increases, the critical speed decreases slowly at first and then decreases rapidly. Moreover, in case of greater twisting moment, the critical speed decreases more rapidly withth e increases of the thrust and own weight.
2) If the other conditions are same, the value of the critical speed is greater in case of the rod with fixed-fixed supports than in case of that with fixed-simple supports. However, the behavior of the critical speed with variation of the above-mentioned parameters is almost same in both cases.
3) The range of the critical speed pertaining to each lateral-vibration mode is limited by the thrust, own weight andt wisting moment if the physical property of the rod is constnt.
4) The critical speed decreases with an increasing mass-ratio, M, which is the ratio of the mass of the circumferentialfl uid to that of the rod. In case that the dimension-ratio, which is the ratio of the outer radius of the rod to itsl ength, is less than 0.01, the ratio, c, of the critical speed of a rod rotating in a fluid to that of the same rod rotating in the vacuum (probably, in air) could be estimated by the following equation: c= (1+M)-1/2.
5) The critical speed calculated by the theory developed in this report gives a higher value by about 14% than the actual value because of slight unsimilarity in the supports of the rod. However, the obtained relationships between the critical speed and other parameters are considered to provide a valuable aid to operate the machinery for an off-shore boring and to design the rod.

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Agglomerates growth in turbulent flow is theoretically investigated. Coalescence probability in the process of agglomerates growth is formulated on the basis of Kolmogoroffs theory under the assumption that agitation field is in an isotropic turbulent flow, and also on the basis of physical properties of agglomerates. And characteristic diameter (C_D) of agglomerate is defined as a diameter at which coalescence probability of two agglomerates in the same diameter is zero, and C_D is generally expressed by Eqs.(34) and (35). A population balance equation is constructed using the collision frequency function based on the Kolmogoroff s theory and the coalescence probability.
Simulation results are as follows:(1) Regardless of variation of cw/w₁, cumulative size distributions normalized by each weight mean diameter approach a specified distribution curve with lapse of agglomeration time, within a limitted time in the R>λν.
(2) C_S is proportional to C_D.
(3) Accordance with the results of (1) and (2), it was proved that it is capable to predict the cumulative size distribution at steady state.
(4) When CD suddenly increases in agglomeration process, growth pattern of agglomerates changes from slow growth to rapid growth.
(5) lf σst is equal to Qt arid the saturation degree is relatively high, CD is expressed by Eqs.(50) and (51). And also, CD is given by Eqs.(52) and (53), when each of B₁ and B₂ in Eqs (50) and (51) is kept constant and ε is proportional to N³. The following characteristics in the agglomeration are theoretically proved from Eqs.(52) and (53).
i) C_D increases, as γ, cosθ and ψ_B, increase, and as γ andε decrease. The effect of these factors on the C_D is larger in R>λν than in R>λν.
ii) On the fixed condition of N, agglomerates growth rate becomes faster, as γ, cosθ and ψ_B and N (0) V increase, and as ε decreases. ln the cases resulting the same C_D at different N, the higher N, the faster in agglomerates growth rate.

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The state of chromium, the size distribution, microscopic texture, chemical composition, lattice constant, and specific gravity of chromite in the lateritic nickel-leached residue of Nonoc refinery (Philippines) were investigated. The results obtained are summarized as follows:(1) The state of chromium in the lateritic residue. There are two kinds of chromium, one is insoluble and the other is soluble to HCl. The former exists as chromite, the latter is contained in ironoxide as substitutional element.
Total chromium content shows the maximum value at the size range of 74 to 150m and it decreases with increase or decrease in particle size. Chromium % as chromite in total chromium of the plus 37μm portion is 70 to 80%, on the other hand, that of the minus 37μm is approximately 33%.
(2) Size distribution of the chromite particles. The absolute size constant (d') and dispersion constant (n) obtained fromRosin-Rammler graph are 73μm and 1.3, respectively. Weight % of the minus 37μm portion is 33.
(3) Three groups of chromites found in the lateritic residue.
a) Micrdscopic texture: Polished sections showed that A group isalmdst flat and homogeneous, B group has many waved cracks, and C group is porous.
b) Counts % of each group: A is about 90, B is about 10, and C is 1 to 2%.
c) Chemical composition: A, B, and C groups correspond to Aluminian chromite (average Cr/Fe ratio 2.5), Chromian spinel (average Cr/Fe ratio 1.7), and Ferrian chromite (average Cr/Fe ratio 1.3), respectively.
d) The calculated valuesoflattice constant (ao) ancespecific ogravity (S. G.): A group a₀ 8.230-8.292 Å(average 8.246Å) S. G. 4.35-4.70 (average 4.52) B group a₀ 8.152-8.228Å, (average 8.182Å) S. G. 4.00-4.35 04.19) C group a₀ 8.303-8.352Å(average 8.345Å) S. G. 4.70-5.00 (average 4.92)

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Measurements of elimination rate of iron have been carried out by addition of K₂ SO₄, Na₂SO₄, or (NH₄) ₂SO₄ to the leaching solution of zinc ferrite residue producted in hydrometallurgical zinc process.
A small amount of precipitation was producted in the leaching solution without any addition of alkali sulfate only by the treatment of pH conditioning and heating. This precipitation was found to be amorphous S-Fe0.OH, and filtration property was poor.
The elimination of iron was improved with formation of jarosite by addition of alkali sulfate. The elimination rate of iron increased with elevating temperature. Potassium jarosite have the best effect upon the elimination of iron among the three kinds of jarosite. Good crystallinity of each jarosite was observed with scanning electron microscope. Good filtration property of jarosite seems to be due to the good crystallinity.
The precipitation reaction of iron in jarosite method was indicated to follow the following rate equation of 2 order reaction._??_k₂; rate constant, t; time, a; Fe₂ (SO₄) ₃ concentration, b; M₂ SO₄ concentration, x; formation amount of jarosite. Activation energy of the reaction for each jarosite was calculated as follows, Potassium jarosite; 5.43 kcal/mol 22.73 kJ/mop Sodium jarosite; 8.394 kcal/mol 34.96 kJ/mop Ammonium jarosite; 16.675 kcal/mol (69.81 kJ/mol)
From the aspect of the kinetics, addition of K₂SO₄ is favorable to the elimination reaction of iron.

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Generally, to raise the level of pulp density in leaching, affects on the extraction of Ni, Fe and MgO, so that it makes necessary to change the levels of the other factors to gain the high Ni extraction rate. To obtain the highNi extraction in high pulp condition, a series of experiment were carried out by using the experimental planning method, andby changing the factors in leaching. The factors adopted were (1) pulp density, (2) concentration of H₂SO₄, (3) leaching temperature, (4) leaching time, (5) NaF addition to solution, (6) agitation velocity in solution.
The results obtained were as follows:
(1) Optimum condition in leaching to extract Ni
(d) time: 150 min
(a) NaF addition: 0.04 g/g-ore
(e) agitation velocity: 500 rpm
(b) concentration of H₂SO₄: 5.0 N (f) pulp density: 100 g/1 (c) temperature 82°C

(2) Extraction rate and ion concentration of leached solution in optimum condition
(a) Ni: 95.0% Fe: 94.5% MgO: 94.2%
(b) Ni: 1.2 g/l Fe: 6.8 g/l Mg: 7.3 g/l

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