Crushing

Because transport costs often exceed the production cost, it is important for the quarry to have good road, rail and/or water transport links and for the most appropriate and cost-effective form of transportation to be used. 

It is usual to carry out crushing in two or three stages, because of the limitations of the various designs of crusher, such as  

In most operations, crushers are selected with care to produce the required amounts of aggregate-sized particles, without over-production of fines (below 3 mm and including dust). Where large amounts of fines are required, impact crushers are often used. When impactors cannot produce the required fineness, it becomes necessary to grind the limestone. 

Jaw crushers tend to produce slabby particles, particularly when operating at high reduction ratios. Where slabbiness is an issue, it can be reduced to a certain extent by using profiled jaws and by operating at lower reduction ratios. 

Impactor crushers consist of a lined crushing chamber inside which a rotor revolves on a horizontal axis. Attached to the rotor are either swing hammers or fixed blow-bars (Fig. 5.4). Stone enters the crushing chamber down the feed chute and is broken by impact with the hammers/blow-bar and with the breaking plates. Reduction ratios of up to 20 1 can be obtained. More complex crushers with double rotors can give ratios of 40 1. 

---

This cement is very resistant to attack by sulphates, sea water and acid waters. It is also used with crushed firebrick to produce refractory concrete. 

SWS are useful to obtain direct indications of hydrocarbons (under UV light) and to differentiate between oil and gas. The technique is applied extensively to sample microfossils and pollen for stratigraphic analysis (age dating, correlation, depositional environment). Qualitative inspection of porosity is possible, but very often the sampling process results in a severe crushing of the sample thus obscuring the true porosity and permeability. 

In a more recent development a new wireline tool has been developed that actually drills a plug out of the borehole wall. With sidewall coring (Fig. 5.36) some the main disadvantages of the SWS tool are mitigated, in particular the crushing of the sample. Up to 20 samples can be individually cut and are stored in a container inside the tool. 

Apparently a negative AP with Q < 90° can be found for particular pore geometries [53]. A different type of water repellency is desired to prevent the deterioration of blacktop roads consisting of crushed rock coated with bituminous materials. Here the problem is that water tends to spread into the stone-oil interface, detaching the aggregate from its binder [54]. No entirely satisfactory solution has been found, although various detergent-type additives have been found to help. Much more study of the problem is needed. 

A very important but rather complex application of surface chemistry is to the separation of various types of solid particles from each other by what is known as flotation. The general method is of enormous importance to the mining industry it permits large-scale and economic processing of crushed ores whereby the desired mineral is separated from the gangue or non-mineral-containing material. Originally applied only to certain sulfide and oxide ores. 

Prior to about 1920, flotation procedures were rather crude and rested primarily on the observation that copper and lead-zinc ore pulps (crushed ore mixed with water) could be benefacted (improved in mineral content) by treatment with large amounts of fatty and oily materials. The mineral particles collected in the oily layer and thus could be separated from the gangue and the water. Since then, oil flotation has been largely replaced by froth or foam flotation. Here, only minor amounts of oil or surfactant are used and a froth is formed by agitating or bubbling air through the suspension. The oily froth or foam is concentrated in mineral particles and can be skimmed off as shown schematically in Fig. XIII-4. 

The gases from the kiln contain about 9% sulphur dioxide. (The calcium oxide combines with the silica to form a silicate slag which, when cool, is crushed and mixed with some anhydrite to give cement, a valuable by-product.)... 

Naphthyl Acetate. CHgCOOCi H,. Dissolve 1 g. of pure 2-naphtnol in 5 ml. (r8 mols.) of 10% sodium hydroxide solution as before, add 10 g. of crushed ice, and i-i ml. (1-14 g., 1 5 mols.) of acetic anhydride. Shake the mixture vigorously for about 10-15 minutes the 2-naphthyl acetate separates as colourless crystals. Filter at the pump, wash with water, drain, and dry thoroughly. Yield of crude material, 1-4 g. (theoretical). Recrystallise from petroleum (b.p. 60-80 ), from which, on cooling and scratching, the 2-naphthyl acetate separates as colourless crystals, m.p, 71 yield, 10 g. 

A) Diazotisation of Anthranilic Acid, Dissolve 20 g. of anthranilic acid in a solution of 7 5 g. of anhydrous sodium carbonate in 200 ml. of water contained in a 400 ml. beaker, (The mixture may be warmed very gently with stirring to obtain a solution more rapidly, and then cooled.) Add slowly 12 g. of sodium nitrite and cool the stirred solution below 10 , Pour this cold solution slowly on to a vigorously stirred mixture of 40 ml, of concentrated hydrochloric acid and 120 g. of crushed ice in a 600 ml. beaker. 

Dissolve 4 5 ml. of aniline in a mixture of 10 ml. of concentrated hydrochloric acid and 20 ml. of water cool the solution to 5°, and diazotise by the addition of 4 g. of sodium nitrite dissolved in 20 ml, of water, observing the usual precautions given on page 181. Dissolve 7 g. of 2-naphthol in 60 ml. of 10% sodium hydroxide solution contained in a 200 ml. beaker, and cool this solution to 5 by external cooling, aided by the direct addition of about 20-30 g. of crushed ice. Now add the diazotised solution very slowly to the naphthol solution, keeping the latter well stirred meanwhile the mixed solutions immediately develop a deep red colour, and the benzeneazonaphthol should... 

Now remove the flask from the water-bath, and slowly add a solution of 5 ml. (5-2 g.) of dry ethyl benzoate in 15 ml. of anhydrous ether down the condenser in small quantities at a time, mixing the contents of the flask thoroughly between each addition. When the boiling of the ether again subsides, return the flask to the water-bath and reheat for a further 15 minutes. Then cool the mixture in ice-water, and carefully pour off the ethereal solution into a mixture of about 60 ml. of dilute sulphuric acid. and 100 g. of crushed ice contained in a flask of about 500 ml. capacity fitted for stearn-distillation, taking care to leave behind any unchanged magnesium. 

Sodium Hypochi ite. zM- This may be prepared with sufficient accuracy by dissolving 100 g. of NaOH in 200 ml. of water in a large beaker, cooling the solution, and then adding about 500 g. of crushed ice. Now counterpoise the beaker on a rough set of scales, and pass in chlorine from a cylinder until an increase in weight of 72 g. is obtained. Make up the solution to i litre and stir well. The solution must be kept in a cool dark place, but even then slowly decomposes. 

It is often necessary to obtain temperatures below that of the laboratory. Finely-crushed ice is used for maintaining the temperature at 0-5° it is usually best to use a slush of crushed ice with sufficient water to provide contact with the vessel to be cooled and to stir frequently. For temperatures below 0°, the commonest freezing mixture is an intimate mixture of common salt and crushed ice a mixture of one part of common salt and three parts of ice will theoretically produce a temperature of about — 20° but, in practice, the ice salt mixtures give temperatures of — 5° to — 18°. Greater cooling may be obtained by the use of crystalline calcium chloride temperatures of — 40° to — 50° may be reached with five parts of CaCl2,6H20 and 3 5-4 parts of crushed ice. 

Hydrobromic acid. Method 1 (from bromine and sulphur dioxide). A mixture of 600 g. (or 188-6 ml.) of bromine, 250 ml. of water and 760 g. of crushed ice is placed in a 1 6 litre round-bottomed flask and a rapid stream of sulphur dioxide (from a siphon of the liquefied gas) is passed into the flask, care being taken that the outlet of the gas-delivery tube is below the surface of the bromine layer. The rate of flow of the gas is adjusted so that it is completely absorbed. It is advisable to cool the flask in ice and also to shake the contents from time to time. The reduction is complete when the mixture assumes a uniform yellowish-brown or yellow colour, which is unaffected by further introduction of sulphur dioxide excess of the latter gas should be avoided as it will be... 

Now run in a solution of 52 g. (53-5 ml.) of pure diethyl carbonate (1) in 70 ml. of anhydrous ether, with rapid stirring, over a period of about one hour. A vigorous reaction sets in and the ether refluxes continually. When the diethyl carbonate has been added, heat the flask on a water bath with stirring for another hour. Pour the reaction mixture, with frequent shaking, into a 2 litre round-bottomed flask containing 500 g. of crushed ice and a solution of 100 g. of ammonium chloride in 200 ml. of water. Transfer to a separatory funnel, remove the ether layer, and extract the aqueous solution with two 176 ml. portions of ether. Dry... 

Place 0 -5 g. of 3 4 5 triiodobenzoyl chloride in a small test-tube, add 0 -25 ml. of the alcohol - ether and heat the mixture gently over a micro burner until the evolution of hydrogen chloride ceases (3-5 minutes). Pour the molten mass into 10 ml. of 20 per cent, alcohol to which crushed ice has been added. Some derivatives solidify instantly those which separate as oils change to solids in a few minutes without further manipulation. Recrystallise from rectified spirit (use 50 per cent, alcohol for esters of methyl and butyl carbitol ). 

---