Recently, we have taken a growing interest in the development of offshore placer minerals such as sand, black sand etc. in Japan. It seems that only a vibrocorer is a useful sampler to get a long and undisturbed core from unconsolidated placer deposit. Reports of the fundamental data to design a vibrocorer have not been published to date apparently, in spite ofne cessity of their data. To obtain the fundamental data, we carried out some basic studies and obtained the results as follows:
(1) it is comparatlvely easy to penetrate more than 5 meters of unconsolidated sand strata
(2) in this case, the whole weight of the vibrocorer, the force of vibration and the way of producing vibration are the effective factors,
(3) there exist the optimum values of these factors.
(4) under the conditions of the forces of vibration beeing kept same, the heavier the weight of the umbalanceis, the more rapid the penetrating rate is.

View full abstract

It is very important for mine safety to inspect the rock mass around underground openings. In this study, the rock mass above the hanging wall which had been supported by the pillars was inspected with the progress of themining of the pillars. The inspection was performed by monitoring the propagation velocity and the attenuation of the amplitudeof the sonic wave through the rock mass. A portable equipment to observe a cracking in a rock mass by means of thechange in the amplitude of sonic wave was made and used for the detection of crackings. The observation started before thebeginning of the mining of the pillars and continued for about two years until the pillars were mined out. The experimentalresults are briefly shown below.
1) Pwave velocity does not change throughout this experimental period.
2) The attenuation of the amplitude of the sonic wave increases in conjunction with the progress of themining of the pillars, and the increase of the attenuation is going to stop when the pillars have been mined out and theopening areah as been filled up with soil.
3) History of the attenuation shows that the rock mass under inspection settles under the condition thatthe pillars have been mined out.

View full abstract

Studies have been carried out on the explosions of coal dust-methane-air mixtures of relatively high dustconcentration, using an apparatus developed by authors, which can generate sufficiently uniform dust clouds in therequired range of dust concentration. Coals used are listed in Table 1.
The most characteristic phenomenon observed is that explosion occurs at higher dust concentrations thanthe upper explosion limit of a coal, while explosion never occurs at a higher methane concentration than the upper explosion limit of methane. Thus the explosion region forms a peninsula in the figure. A typical explosion limit curve isshown in Fig. 2. Effect of particle size, on the upper explosion limit of the mixture is large as shown in Fig. 3.
Figure 4 shows the curves of explosion limit for Horonai, Russel Fork and K-10 coals of 270-400 mesh insize. In the explosiye region of methane (5 to 15 pct), there is no considerable difference between them, whiledifference is found in the region of methane concentration less than 5 pct.
As an extreme case where volatile content is near 100 pct, Fig. 5 shows the upper explosion limit curve ofpotato starchmethane-air mixture. In this case the peninsula is not formed. This may suggest that further increase ofvolatile content of coals could cause the disappearance of the peninsula. This limit volatile content was estimated using theequation in the text, which was obtained from experimental results shown in Fig. 6, and ca. 60 pct volatile content was obtainedfor 270-400 mesh coal. As another extreme case, explosion limits of stone dust-methane-air mixtures are shown in Fig. 7.

View full abstract

This work has been undertaken to demonstrate an inhibiting effects of some surfactants on spontaneous combustion of coals. Ignition temperature of coals, carbon monooxide production and oxygen consumption during an oxidation process of coals co-existing with surfactant were measured.
The conclusions drawn from these experiments are as follows;
1) Some surfactants have a certain good influence on ignition temperature of coals, but the magnitude of rising trends are different with varieties of surfactant and coal.
2) In oxidizing process of coals co-existing with a surfactants. a sudden increase in carbon monooxide production were observedatVicertaintemperature (about 150°C). The cafbon monooxide concentration and its production state at that time depended mainly on the used surfactant.
3) Judging from each experimental result, the sudden produciton of carbon monooxide are caused by decomposition of surfactant with consumption of oxygen.
4) A utility of surfactant as an inhibitor can be distinguished in relatively low temperature, In an extent from ambient temperature (room temperature) to about 100°C, the thicker the surfactant are used, the higher the efficiency is.

View full abstract

In order to put a vertical double-belt conveyor into practicaluse, it is necessary to know its conveying capacity and power requirement. Although much information is available for the ordinary belt conveyor, there has beenlittle information forthe vertical double-beltconveyor. In this investigation, the experlmental data, which are reported in the previous paper, are analyzed in order to obtain such information.
The main results are as follows;
1) For vertical double-beltconveyors with roller arrangement that is geometrically sinlilar to that of the experimental apparatus, the maximum sectlonal area of the load is given by the formula;
A=0.04B²
2) The tractive force per span is proportional to the normal load to the rollers whenno materials is conveyed.
3) When nlaterial is conveyed, the additional tractive forceis almost proportional to the sectional area of the load.
4) Whe material is conveyed, the additional tractive force increases with the increase of the degree of offset of the rollers.
5) Running resistance of the belts is generated in different mechanisms when coal is conveyedand when sand is.
6) Overall tractive force can be calculated by the formula;P= {(1+ζ) N-1}{(1+φ) T_o+ψ+η/ζ} +φT_o+ψ,
where T_o is the minimum tension of thebelts, N is the number of spans, and φ, ψ, ζ and ηare coefficients given as functions of the sectional area of theload, the trough angleand the degree of offset.

View full abstract

In order to disperse the clayey fine particles obtained from the disintegrated weathered granite in dry system, the authorsh ave performed sieving tests, observations of particle surface and measurements of powder characteristics, using the samplesb efore and after addition of metallic stearate. The results obtained are summarized as follows:
(1) From the degree of dispersion of sample, the optimum mixing time of the clayey sample with stearate was proved to be 5 minutes in the case of sample weight 70g in 800ml vessel a batch and mixing speed 14000r. p.m.
(2) Th e sieving of clayey sample through fine mesh in dry system were promoted notably by adding the metalic stearate. E specially, the most effective rates of addition were 3% of Mg-stearate and 5% of Na-stearate.
(3) Through the SEM observation, it was recognized that the many very fine particles agglomerating onto the surface of rather coarse particles were dispersed and removed by addition of the stearate, replacing partially those fine particles.
(4) Th e effect of addition of metallic stearate on the dispersion of the sample seems to be related to the adhesive forces among the particles. And the positive effect of stearate on promotion of sieving were proved also by the variation of dynamic properties, i. e. compactability or floodability index of the sample.

View full abstract

The femoval of heavy metal compounds from sypthesized waste cyanide water is achievable by a precipitation-flotation method. However, the differential separation of constituting metals by this method was thought to be very difficult.
The authors found that the addition of some decomposing reagents to the synthesized waste cyanide water of cadmium and zinc can modify the separation characteristics of tnese metals. In this paper, the separation of cadmium from zinc in the synthesized waste cyanide water by the preclpltatlon-flotatlon method is discussed. The proposed method was to use sodium sulphide as a decomposing reagent in the first stage of flotation and hydrogen peroxldte in the second stage in order to decompose Cd-CN and Zn-CN complexes, respectively. rurmermore, the use of such Cation flocculant as FC-80 was considerably ettective for the removal of Cd-CN complex.
Based on a series of fundamental flotation tests, actual differential flotation tests were made. The senaration of endmium from Zinc in the synthesized waste cyanide water was found to be satisfactory.
Tnis memod can be effective for the removal of ditfficult-to-separate colloidal precipitates from liquids by the sedimentation method, provided the applicability of this method to the separation of the other metals is promising. this consists of the intensive studies which have been conducted at authors' laboratory.

View full abstract

Distribution ratios for Ni, Co, As and Sb between silica-saturated slag and matte were determined at 1300° under a current of 1 or 10 per cent SO₂ gas. As illustrated in Figs.1 and 2, these elements tend to cocnentrate in matte phase, but to be oxidized into slag at higher matte grade corresponding to higher oxygen potentials. As shown in Fig. 3, dissolution of copper in slag is greatly influenced by the contents of sulphur and lime in slag, and is reasonably explained by complexdi ssolutions of oxidic and sulphidic copper in slag. The similar explanation is successfully adopted also for distribution behaviour of nickel. Combining the present data with those obtained previously under metal saturation, the effects of oxygen potential and matte grade on the distribution ratios are discussed.

View full abstract

Conditions of the attainment of equilibria between CO₂-CO gas mixtures and iron-silicate slags wereinvestigated in regard to grinding procedures in chemical analyses of slags and emf measurements using the magnesi astabilized zirconia electrolyte.
It was found that the analytical error in determining the ferrous and ferric oxides in slags increased because of oxidation of samples during grinding in an agate mortar.It was also found that, in the cases of experiments in which molten slags were equilibrated with CO₂-CO gas mixtures by permitting gas mixtures to flow over the melt, an equilibrium was easily attained by oxidizing the slags with the gas mixtures, whereas it took too long a time for an equilibrium to be established by reducing the slags.

View full abstract