Up to date, the greater part of precipitates formed during the neutralization of mine drainage has been discharged into tailing dams. This fact is causing a serious problem concerning the life of dam, by the reason of that the precipitate is very voluminous and requires considerable space.
Accordingly, it can be said that the most effective solution for above-mentioned problem is to accelerate the utilization of precipitate.
In order to offer a technical information to various trials concerned with utilization of the precipitate, in the present paper, this research committee has reviewed about the following subjects of the material.
1) Physical and chemical properties.
2) Properties related to mineral processing such as handling property, fl oatability and property of agglomeration in water.
3) Practical examples of utilization and usability.

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This paper was written for my memorial speech of the Watabane Award at the general meeting of MMIJ on the 31st of March, 1981.
The author has an image that Ezuri is the simplest mine.
In order to explain how to build such a simple mine, the author mentions the history of the mining technology on the KUROKO-mine, which Dowa Mining Co., Ltd. has developed for about 20 years, especially underhand horizontal slicing with artificial mortar-roof, Trackless mining and belt conveyor system, raise machines and the rest.

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Each colliery under different geological conditions has accumulated the original know-hows in mining methods, safety measures, etc.
These know-hows have been developed through continuous study and various experiences for a long time.
In the Akabira colliery, under inferior mining conditions due to steeply inclined strata and existence of many faults and folds, we have struggled against spontaneous combustion and gas outburst since opening the mine.
Several noteworthy know-hows mentioned below have been developed in our colliery and their details and developing process are described in this report:
(1) Countermeasure to gas outburst by the execution of release boring with a diameter of 200 mm to 250mm;(2) Drilling technique for large diameter holes (75mm-1, 500mm), so-called “The large diameter ring shaped boring”
(3) Centralized monitoring system with the tube bundle for the early detection of spontaneous combustion;
(4) Fly ash slurry transportation and filling system from the operation plant installed on surface;
(5) Mechanized longwall mining system for steeply inclined coal seam; and
(6) Operation of fluidized-bed combustion boiler.

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Fixing our eyes upon the size distribution characteristics of fragments by blasting, we made experiments on crushing of uniform size cubic blocks which are made of cement mortar. The results obtained with the good reproducibility are as follows,
1) Rosin-Rammlar-Bennt diagrams of all blasting fragments were made of straight lines, so we admitted that the sizedi stribution of fragments may be characterized by Rosin-Rammlar distribution function.
2) With constants which were found from lines for each fragment, namely the size distribution constant (n) and the absolute size constant (De), we calculated mean particle size (Dp) and specific surface area (Sw) through
Dp=Deγ(1/n+1)
Sw=Φ/ρ_p·10⁴·1/De {γ(1-1/n)-0.0010 (1-1/n)}/1-(1/n)
where Φ= specific shape factor of crushing products which are given surface shape factor (φs) and volume shape factor (φv) through Heywood's method, ρ_p=density of crushed particles.
3) From optimum straight line through our experimental data, we found out following formulas,
a) The relation between the mean particle size and charge depth (W).
D_p=206-33.2·InW
b) The relation between the specific surface area ratio and charge depth one,
S_N/S_w0=4.72e1.40 (W/W₀)
where S_W0=specific surface area of original block, W₀=max. charge depth, distance of center of block.

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This paper presents the prediction method for time-dependent development of the ground movements in natural gas field.
The analytical method we used is almost similar to that of 1st report. But, in order to take the time-dependent change of piezometric head in gas seam, Theis equation for unsteady flow to a well is used. It is found that Theis equation can be fully applied to ‘gas well’ and the calculated results agree well with the actual measurements.
And also, in order to take the influence of depth of gas seam upon the ground movements, finite element analysis is carried out.
So, the following results were obtained.
Increasing the depth of gas seam, the values of ground movements decrease, when the drawdown curve in gas seam is same in all cases.
The vertical ground movement (surface subsidence) which is given by our analytical method is slightly different from the profile with finite element technique, but it is sufficient to understand the outline of subsidence in natural gas field.
Finally, we find that the ground movements in natural gas field consist of the vertical and horizontal components. So, in natural gas field, we must consider not only the surface subsidence but also the horizontal ground movement.

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The air pollution with Benzo (a) pyrene B (a) P has been turned to be the & reat part of pollution problem, for B (a) P is recently suspected to be carcinogen. The author studied the air pollution with special emphasis on B (a) P in the mine air several years ago. In this paper he has a discussion on several analytic results of B (a) P pollution in four mine air.
The analytical process is as follows.
a) The collection of airborne dust by middle volume air sampler (500 l/min) making use of the cylindrical glass fiber filter (95φ×210mm).
b) The selective extraction of polyaromatic hydrocarbon by the Soxhlet.
c) The separation of the extractive materials into each chemical components by one dimensional dual band thin-layer chromatography.
d) The identification and determination of the separated chemical components by spectrofluorometry. This method is ordinary used to analyze B (a) P in the mine air. The results are as follows.
1) B (a) P content in the mine air polluted by the afterdamp is 0.60-4.64μg/1000m³. This content is equal to the urban air of Morioka, and in other words, is about two times as high as those in the natural back ground air, and is about a tenth part smaller than those in Tokyo or Fukuoka urban air.
2) As compared with the Maximum Non-carcinogenic Doses of B (a) P proposed by Hammond (1970), B (a) P content in me mine air is within the extent of high safety.
3) As a result of the experiment, moreover, it has been recognized that the most effective defence against B (a) P carcinogen is the use of the dust mask in the mine.

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A continuous sieving device and an air separator were newly designed, the former has air and mechanical vibrator to separate fine particles from disintegrated weathered granite by sonic waves and the latter has zigzagged tube of whic warping angle is changeable to separate them by air. The performance of these two devices was examined and their optimum operating conditions were investigated. The results obtained are as follows.
1) The optimum conditions of sonic waves cycle at each sieve onenino size for the sieving device were obtained as follows:
37μm; 75Hz; coarser than 74μm; 60Hz. The Newton process efficiency under these conditions were 67, 79, 83 and 93% at the sieve opening sizes of 37, 74, 149 and 297μm respectively
2) The optimum warping angle of zigzagged tube of the air separator were 25-35° for the separating particle size of 37μm, and 35° for that of 74 and 149μm. The Newton process efficiency under these conditions were 67, 81 and 93% at the separating particle size of 37, 74 and 149μm respectively.
3) These two devices gave almost the same Newton process efficiency at the fine senaratino narticle Size of 17 and 74μm under the test conditions.

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An electrochemical technique, which has been established previously, was adopted to investigate the origin of a Cu₂O phase often detected in the anode residues in copper electrorefining.
It has been found that a Cu₂O phase in the slime layer originated from the surface of a corroding anode. Therefore, when oxygen content increases in the copper anode, an amount of Cu₂O entering the slime layer correspondingly increases; thus making it thicker. This causes the mass transport of Cu²⁺ ions from the surface of a corroding copper anode to be more restrictive, and, in turn, the tendency of the anode to passivate increases.
Material balance calculations have shown that about 3 to 5% of Cu₂O in the anode enter the slime layers when a large variety of copper anode samples were anodically dissolved under the nominal testing conditions. This ratio was observed to further increase to about 8% when one particular anode sample contained 7300 ppm oxygen.
A Cu₂O phase present in a layer of anode slimes, when contacted with a sufficient amount of oxidizing agent such as dissolved oxygen, is expected to dissolve actively according to the chemical reaction,
Cu₂O+2H₂SO₄+1/2O₂→2CuSO₄+2H₂O (ΔG°=-47.3kcal/mol)
The addition of a small amount of H₂O₂ to Cu electrolyte increases the oxidizing effect, which agrees with the observed fact that the tendency of anodes to passivate dramatically decreases by this addition as well as by sparging O₂ gas in the electrolyte.

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Various factors affecting the leaching rates of sphalerite in aqueous sulfuric acid solutions were examined. These factors were the iron content of the sphalerite, temperature, the after effect of various flotation agents, and the particle size of sphale- rite. Experiments were also made to compare the leaching rate of sphalerite in a hydrochloric acid solution with that in a sulfuric acid solution.
The leaching rate of sphalerite linearly increased with an increase in iron content. The overall reaction of sphalerite appears to be controlled by a chemical reaction, exhibiting an activation energy of 13.7kcal/mol. The effect of potassium ethyl xanthate and pine oil on leaching rates were found to be negligibly small. On the other hand, leaching of sphalerite activated by cupric sulfate appeared to be greatly retarded. However, this decreased leaching rate of Cu-activated sphalerite was readily recovered by de-activating the sphalerite with sodium cyanide.
Another important factor which affect the leaching rate was particle size. Based upon these experimental results, excess fine grinding is not effective for the leaching of sphalerite evolving hydrogen sulfide gas. The leaching rate of sphalerite in a hydrochloric acid solution without the addition of soluble chlorides was found to be slower than that in a sulfuric acid solution.

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Mikkaichi Smelter of Nippon Mining Co., Ltd. which is an electro-thermic zinc smelter, employs Weaton-Najarian vacuum condenser in order to condence zinc vapor in it.
The existing condensers were so small that their condensing efficiency of zinc vapor could not be kept high and “Clean-out work” was required often.
A model experiment using water was made for the purpose of determining the optimum specification of the condenser to be installed.
The following improvements have been performed by renewing the condensers on the basis of the experimental results.
1) Electric power saving
2) Man power saving
3) Maintenance cost saving

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Zinc sulfide pellets were reacted with steam to obtain elemental sulfur and zinc oxide. Addition of an appropriate amount of oxygen to steam was found effective for the purpose. Addition of neither hydrogen to steam nor carbon to zinc sulfide was effective. It has been suggested that zinc oxide formed on the surfaces of zinc sulfide pellets promotes the Claus reaction to form elemental sulfur.

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