The economic benefit accruing from the use of polyacrylamide flocculants for accelerating the precipitation and clarification of the mineral suspensions handled in the beneficiation of minerals depends markedly on the polyacrylamide (PAA) content and its degree of hydrolysis in the commercial product. Practice has shown that polyacrylamide flocculants do not have the same flocculating capacities. One of the most important factors determining the flocculating capacities of polyacrylamides is the configuration of the polymer molecule in the solution [1][2][3], which depends on their degree of hydrolysis, i.e., on the ratio of the percentage content of COO groups x + to the total number of functional groups of the polymer.During synthesis of commercial PAA, some of the amide groups are hydrolyzed to carboxyl groups [2] and neutralized by alkali (milk of lime, ammonia, NaOH). Thus in all cases commercial PAA is a copolymer of acrylamide and salts of acrylic acid, their ratios depending on the method of preparation. The gelatinous PAA solution, produced in our factories, contains up to 10% of pure PAA and up to 18% of impurities (ammonium, potassium, and sodium sulfates).In the manufacturing plants, the PAA content of the final product is equated to the monomer content of the reaction mass before polymerization, although the yield of the polymer depends on the polymerization procedure. The monomer content is determined by bromination of the double bonds [4], which are present before polymerization in both acrylamide and acrylic acid; therefore the degree of hydrolysis in the final product cannot be established.The absence of monitoring of the PAA content and its degree of hydrolysis in the final product at the manufacturing plant is due to the fact that existing methods of determining these parameters [2, 3, 5] are unsuitable for analysis of the commercial product, which contains up to 16% of ammonium sulfate. This paper gives a method for determining the content of PAA and its hydrolyzed part in commercial ammoniacal PAA (from the Leninsk-Kuznetsk Semicoking Factory), containing up to 16% of (HN4)zSO4, which makes it the most difficult type to determine. The (NH4)iSO a content of PAA was determined from the SO~-ion by quantitative precipitation with BaC12 from a 0.05% hot acid solution; it was 15.3%.Procedure. A weighed sample of commercial gelatinous PAA was dehydrated in acetone, the free ammonia being removed during this process. The impurities, mainly (NH4)2SO4, were then removed by repeated leaching with aqueous acetone until BaC12 gave a negative reaction for the SO l" ion. The concentration of the aqueous solution of acetone was selected experimentally so that the impurities, but not the PAA, dissolved. Drying at 70~ gave a residue of 9.2%; its ash content after baking at 800~ for 2 h was 1.45%. The increase in weight of the solid polymer to 9.2%, as against the standard value of 7.4%, might be due to residual moisture; to the presence of impurities in the iattial product -acrylonitrile; to the presence of co...

The adsorption of the different ions and molecules in a solution depends on the electrical charge of the surface of the minerals undergoing flotation. The hydrophobicity and float, ability of minerals are governed by the adsorbed ions and molecules.From a study of the capacity of a double electric layer in the presence of adsorbed molecules, A. N. Frumkin et al. [1,2] derived a theory explaining the influence of an electrode's electrochemical potential on the adsorption of uncharged molecules.According to these authors, the capacity of a double layer in the field of adsorption is greatly reduced because between the layer's plates an interlayer of a substance is introduced, having a lower dielectric constant than water. A capacitor's electric field resists introduction of a body between the capacitor's plates if the dielectric constant of this body is lower than that of the medium filling the capacitor. The double layer's electric field therefore opposes adsorption of molecules reducing the layer's capacity, but assists that of water molecules. The adsorption of uncharged organic molecules is greater on surfaces with smaller charges, irrespective of the sign of the charge.Wetting with water is poorest at potentials closest to the zero charge, and increases sharply with polarization of the surface.To study the changes in the overall electrochemical potential, a limonite electrode with L = 40 mm and d = 5 mm was turned on a grinding wheel. One end of the electrode was fixed in a holder consisting of a special Plexiglas tube. Contact between the electrode and the current conductor was obtained by filling the tube with mercury.The change in E-the potential jump with changing solution pH-was measured as follows. The electrode was thoroughly cleaned on the grinding wheel in an aqueous suspension of quartz, and washed in distilled water; adhering particles of quartz were removed with filter paper, and it was then placed in a beaker with distilled water. It was placed in the agitation compartment of a flotation machine and treated with an aqueous emulsion of kerosene (500 mg/liter) for 5 min at a given pH. Without removing it from the flotation machine, it was transferred to a beaker to determine E-the potential with respect to a calomel comparison electrode.The solution pH was changed by means of H2SO 4 and NaOH. It will be seen from the change in limonite potential at various pH in an aqueous emulsion of kerosene (see figure) that the surface of limonite treated with such an emulsion has a negative charge. With increasing solution pH the negative potential of the surfaces increases owing to adsorption of the excess free hydroxyl (OH-) ions.H + and OH-ions have a very great influence on the state of the double electric layer of limonite, and, therefore, on its reaction with nonpolar reagents (hydrocarbons).The figure plots the floatability of limonite (size class 0.0'/4 mm) by kerosene (500 mg/liter) with addition of frothing agent (pine oil, 50 mg/liter) in an NIGRIzoloto flotation machine (v = 50cm 3 , n = 2000 rev/min...

One method of increasing the effective action of polyacrylamide flocculant (PAA) in the clarification of suspensions is its preliminary hydrolysis in the presence of NaOH fil-3].Aref'eva et al. [4,5], who discussed the interaction of simple electrolytes with the polyeleetrolytes (PE) K-4, PAK, PAA-1, and Ca-PAA, concluded that these PE undergo ion exchange with the cations of simple electrolytes; the capacity depends on the nature of the electrolyte cation and the composition of the functional groups of the PE. Unfortunately they did not give the chemical compositions of their PE or state whether they contained impurities which might distort the results.We have studied the interaction of PAA with simple electrolytes in relation to their degree of hydrolysis a, using purified specimens of ammoniacal PAA with a= 13 or 69% in 0.1% solutions, by means of potentiometric titration, viscosity measurements, or visually from the state of aggregation of the mixed solutions. A PAA specimen with a = 69% was obtained by artificial hydrolysis of commercial PAA in 1% solution in the presence of NaOH. The PAA specimens were purified and the chemical composition of the flocculants determined by the method in [6]. Flocculants in the H form were obtained by passing their solutions through KU-2 cation-exchange resin. The PAA specimens were chosen so that amide groups predominated in one of them and carboxyl groups in the other. In our opinion, this fiocculant composition makes it possible to distinguish most clearly between the interactions of the flocculants with the electrolytes.In Fig. 1, the solid curves are potentiometric titration curves of 50 ml of 0.1% solutions of two PAA specimens with a = 13 % (specimen A) and a = 69 % (specimen B) versus 0.1N solutions of chlorides and sulfates with univalent, divalent, and trivalent cations; the dashed curves represent the pH changes of 50 ml of distilled water when the same electrolytes are added.The chemical compositions of the PAA specimens in 50 ml of 0.1% solutions were as follows:,,B ~ ~A,t mv' I o

The flotation units of Kuzbass preparation plants handle only medium-rank coals, which have higher flotabilities than hard coals of any other rank.Insufficient work has been done on the flotability of low-rank coals, which are less water-repellent than others, although industrial preparation of slurries of these coals would greatly extend the reserves of coke-and-chemical plants. A recent report has also called attention to the desirability of studying the flotation of low-rank coals [1].Flotation of low-rank coals requires a greater consumption (two-to five-fold) of reagents than for other coals, owing to higher content of functional groups and greater porosity [2].Studies of the flotation of Donbass gas coals have shown that good results may be obtained by combined use of apolar and heteropolar reagents, although the consumption of reagents is then much higher than for coking coals [3]. t~t some cases a reduction in reagent consumption is obtained by pretreating the coal surface with high-viscosity oils, and then adding active heteropolar substances [4]. But nobody has yet found what combinations of apolar and heteropolar substances are technologically and economically best.We have studied the influence of apolar reagents with particular boiling ranges, and therefore particular physical and chemical properties, on the flotation and absorption of low-rank coals. Apolar substances were obtained by distilling petroleum from one of the Tyumen fields. Distillation was carried out by the standard method in a Claisen flask over boiling range 50~ Table 1 gives the parameters of the fractions.The flotation experiments were performed in a machine with chamber capacity 0.5 liter, at peripheral velocity 2.34 m/sec, on coals of different rank (see Table 2).The 0-0.5 mm size class was used for preparation tests; a weighed sample of the coal was wetted with twice the amount of water 12 h before an experiment. The heteropolar reagent was normal hexyl alcohol C6Ht3OH. The apolar substance was added to the flotation chamber at the same time as the alcohol; the contact time of the reagem with the coal was 1 rain. On the basis of preliminary experiments, the consumption of apolar reagent was taken as 1.5 kg/t, while that of the alcohol depended on the rank of the coal. For G and D coals the amount of alcohol added was 0.15 and 0.5 kg/t respectively.An analysis of the experimental data (cf . Table 3) shows that the characteristics of the apolar reagent have a marked influence on flotation. Whereas the petroleum fraction with boiling range 200-250~ has maximum activity in the flotation of G coals, i.e., the results are close to those for coking coal in [5]; in the case of D coals the maximum yield of concentrate is observed when the more viscous apolar substances are used. Maximum yield of floats in the case of D coals is obtained with the petroleum fraction with boiling range 300-350~ the use of high-and low-boiling hydrocarbons reduces the yield of concentrate. Minimum flotation time was observed in the case of the 200-250~ petrol...

Underground mechanization has greatly increased output per man/shift by reducing the number of men employed underground, but has not led to manless mining. This calls for improved methods for coal extraction.underground gasification is one industrial method of mining in which the state of aggregation of the coal is changed. Other methods currently being tested are the extraction of coal by solvents, its conversion to a plasma, electrochemical attack, and processing by nuclear energy. These methods enables us to convert the solid coal to a liquid state or obtain gaseous products,thereby providing a more effective coal mining technique [1]. t Underground gasification of coal was first suggested by Mendeleev. He gave the process a theoretical basis and showed that it was a practical method. The process is of course essentially as follows: oxygen in various coneentrations and steam are fed to a combustion site in a coal seam, thereby producing a great amount of producer ga.~ which is piped to the surface.Underground gasification makes it far cheaper and easier to utilize the energy in coal. Furthermore, seams too thin to be worked by conventional methods (i.e., less than 0.5 m) can be utilized [2]. Work on underground gasification of coal is in progress in Belgium, Britain, the United States, Italy, France, and Poland. It should be mentioned that many countries are utilizing Soviet experience in this field [3]. There are. already underground gasification sites in the Moscow, Kuznetsk, Uzbekistan, and Donets Coalfields. This method completely eliminates conventional pit work; the men are mainly engaged at handling semiautomated drills, sinking pipes in boreholes, erection and fitting, and inspecting waterpipes and gas pipes [3].The performance of underground gasification plants could be improved by increasing their capacity and the scale of the work, by rational location of sites, and by improving engineering methods and individual stages of the process.Underground gasification is not the only shaftless method for underground processing of solid fuel.For conversion to high-grade liquid fuel, coal is subjected to destructive hydrogenation, one of the most efficient methods of chemical processing of coal.Hydrogenation consists in direct saturation with hydrogen or splitting of high-molecular coal compounds and addition of hydrogen to the products thus obtained. This gives low-molecular hydrocarbons, used as motor fuel. Addition of hydrogen to coal is promoted by high temperature (400-450~ and pressure (up to 700 arm), and hightemperature stable catalysts (nickel sulfide, tungsten sulfide, molybdenum sulfide, etc.). An increase in hydrogen pressure 9 1000 arm greatly increases the velocity and degree of hydrogenation [4]. In the destructive hydrogenation process the coal is precrushed, the powder mixed with heavy oil, and then subjected to hydrogenation in 2 to 3 stages; this makes for more efficient manufacture of liquid fuel.The underground production of liquid fuel from coal by hydrogenation is described in [5]; at a ...