Kazakh National Research Technical University named after K. I. Satpayev, Almaty, Kazakhstan:

N. K. Dosmukhamedov, Professor of a Chair “Metallurgy and Dressing of Mineral Resources”, e-mail: nurdos@bk.ru
E. E. Zholdasbay, Senior Researcher of a Chair “Metallurgy and Dressing of Mineral Resources”
G. B. Nurlan, Engineer of a Chair “Metallurgy and Dressing of Mineral Resources”

In work with the use of a new precision design of the zone melting unit, which allows to regulate the main parameters of the process (width and velocity of the molten zone), technological experiments were carried out to obtain ultrapure copper, depending on the temperature distribution. Peculiarities of the behavior of impurity metals and the laws governing their distribution between the solid and liquid phases are established under conditions of a change in the width of the molten zone and high gradients of the temperature gradients 1183, 1233 and 1283 ^оC. It has been found that the number of passes equal to four and the ratio of the width of the liquid zone (X) to the total length of the rod (L), X/L = 0.15, is sufficient conditions to achieve an ordered distribution of impurities along the rod within the entire range of temperature variation without the time of exposure to liquid zone. It is shown that the best results for the purification of copper from impurities are reached at a temperature of 1233 ^оC, exceeding the melting point of copper at 150 ^оC. The absolute decrease in the total concentration of impurity metals at this temperature was 371.68 ppm. The copper content in the final purified copper matrix corresponds to 5N3 (99.9993%). On the basis of a change in the concentrations of impurity metals, the distribution coefficients of impurity metals were calculated in the range of reduction of the ratio with X/L= 0.35 to X/L = 0.15. The high values of the metal distribution coefficients at Xi/L = 0.35 and their decrease in the Co, Ni, Fe, Mn and As series are established: K_Co = 8.0; K_Ni = 6.33; K_Fe = 4.4; K_Mn = 3.0; K_As = 1.0. It is not possible to achieve deep copper purification from Co, Ni, Fe, Mn, B, and As in the production of ultrapure copper by zone melting. In this case, an increase in the copper content in the matrix of purified copper must be achieved by deeper cleaning of other impurity metals present in the initial copper to be purified. It is established that the designed design of the plant allows to regulate a number of such important parameters of zone melting as the temperature of the molten zone, the spreading of the boundaries of the liquid zone, diffusion in the liquid zone by imposing a magnetic field. Flexible regulation of these parameters makes it possible to achieve deep segregation of volatile metal impurities even at sufficiently high values of the ratio X/L = 0.35. It is shown that a sufficient degree of segregation for a number of volatile metal impurities (Pb, Bi, Ag, Sn, P, Sb, Zn) is observed at a ratio of X/L= 0.35 due to their high vapor pressure elasticity, compared to copper. A deeper degree of purification of copper from them is achieved at a ratio of X/L = 0.15. Moreover, in the range of reduction of the ratio with X/L = 0.35 to X/L = 0.15, their concentrations undergo slight changes. It has been established that a decrease in the ratio X/L in the range from X/L = 0.35 to X/L = 0.15 significantly affects the change in the concentrations of impurity metals having a distribution coefficient K > 1 (Fe, Ni, Co, Mn, As). It is shown that the behavior of this group of impurity metals under conditions of high temperature of 1233 ^оC is associated with their interaction with each other and the formation of a number of chemical compounds that concentrate in the solid phase and create a convective flow that prevents the equipartition of each separately taken impurity from the liquid zone in solid phase. This phenomenon reduces the degree of purification of copper from this group of metals.

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