Extraction of Non-ferrous Metals as Inorganic Chlorides from Waste Lead Slags in the Presence of Chlorine-containing Components of a Distilled liquid

The presented article contains the research results on extraction of non-ferrous metals as inorganic chlorides from waste lead slags in the presence of chlorine-containing components of a distilled liquid–calcium and sodium chlorides. The research was implemented by a thermodynamic modelling technique using a software package HSC-5.11 Chemistry, based on a Gibbs energy minimum principle, and also a rototable second-degree method of planning an experiment (Box-Hunter method). It was found, that at equilibrium conditions lead is extracted from slags by chloride sublimation the most effectively, then zinc and copper: at pressure of 1 bar and temperature of 15000C the chloride sublimation degree for lead makes 98.63%, for zinc – 64.45% and for copper – 21.91%. To achieve the 95-100% lead chloride sublimation degree the necessary temperature is933.7-13000C and lgP should be from –0.48 to –1.75 (pressure of 0.33-0.0177 bar); for achievement of the 90.0-100% chloride sublimation degree for zinc respective parameters are T=1279.3–15000C and lgP from –0.972 to –2 (pressure of 0.107-0,01 bar), for copper temperature of 1337.7–15000C and lgP from –1.418 to–2 (pressure of 0.038-0.01 bar). It was experimentally proved, that at the sinter-chlorinating roasting at temperature of 1150-11800C and pressure of 0.006-0.001 bar the chloride sublimation degree for lead makes 93-98%, for zinc 82-96%, for copper – 73-88%. keywords: Fuming slags, Distilled liquid, Sodium and Calcium chlorides, Thermodynamic modelling, Sinter-chlorinating roasting, Chloride sublimation of lead, Zinc and copper.


INTRODUCTION
The ammoniac way prevailing in the world soda production gives a considerable quantity of a liquid waste product -distilled liquid.Its composition, g/m 3 : CaCl 2 -118-125; NaCl-58.6-80;CaCO 3 -6-15; CaSO 4 -2-2.7;Mg(OH) 2 -3-10; CaO-2-4; Fe 2 O 3 +Al 2 O 3 -1-3; SiO 2 -1-4 1 .There are some directions of partial recycling of the distilled liquid that allows obtaining: waterless calcium peroxide used for production of bleachers and disinfectants and for treatment of waste water and gas emissions 2 ; phosphorus-containing fertilizers applied in agriculture 3 ; ammonium chloride, which can be used in the textile industry, pharmaceutics, at soldering of metals, tinning, for filling of galvanic cells, as a nitric fertilizer 4 ; high-quality chemicallyprecipitated calcium carbonate widely used in many industries for manufacturing various composite materials 5 .After special preparation the distilled liquid can be applied for pumping in oil wells for the purpose of maintenance of strata pressure 6 .But such the way of its recycling is possible only if soda ash manufacture is situated in the oil recovery area.There is a method of electrochemical processing of the distilled liquid with obtaining Ca(OH) 2 , NaOH and HCl 7 .Also the distilled liquid is used at soda ash manufacturing by means of processing of a salt solution for desulfation of a brine and production of gypsum 8 .We suggest to use the distilled liquid for extraction of nonferrous metals as inorganic chlorides fromfuming slags.
The research was implemented by a thermodynamic modelling technique using a software package HSC-5.11Chemistry, based on a Gibbs energy minimum principle 9 , and also a rototable second-degree method of planning an experiment (Box-Hunter method) 10 .First of all, we studied the pressure and temperature effect on the quantitative distribution of substances in a system under study, and then on the basis of the obtained data -the equilibrium chloride sublimation degree (α chl ) of lead, zinc and copper.The metals' chloride sublimation degree was calculated according to the expression: Where G met (chl) -weight of a metal turned into chloride, kg; G met (in) -weight of a metal in slag, kg.

RESULTS AND DISCUSSION
Temperature and pressure effect on the quantitative distribution of the substances containing lead, zinc and copper in a system slag-(CaCl 2 + NaCl) -O 2 Figure 1 contains the information obtained by means of the software packageHSC-5.11about the quantitative distribution of the substances containing lead, zinc and copper at pressure of 1 and 0,1 bar.As follows from the figure, lead in the studied system is as PbCl 2 , PbCl 2 (g), PbCl(g), PbSO 4 ; zinc as ZnSiO 3 , ZnCl 2 (g), ZnCl 2 and copper as Cu 2 O, CuCl, CuCl 2 (g), CuCl(g).Decrease in the pressure promotes increase in αchl(Me) and reduction of the process temperature.

Temperature effect on the chloride sublimation degree of lead, zinc and copper from the slag in the presence of CaCl 2 and NaCl
Influence of temperature and pressure on αchl(Me)is represented in Figure 2.
Judging from the Fig. 2 the decrease in pressure and increase in temperature leads to increase in α chl (Me).We accept α chl (Pb) >α chl (Zn) >α chl (Cu).

The research matrix and results
The research matrix (according to the second-degree rototableplanning) and results are represented in Tables 1-3.On the basis of the results the regression equations of temperature (T, 0 C) and pressure (lgP, bar) influence on the chloride sublimation degree of lead (α chl (Pb), %), zinc (α chl (Zn), %) and copper (α chl (Cu), %) were obtained: Using these equations according to the technique 11 solid surfaces of temperature and pressure effect on α chl (Pb),α chl (Zn) and α chl (Cu)and their horizontal sections were constructed (Fig. 3).As follows from Fig. 3, α chl (Pb) from 95 to 100% is observed in the area abcd, α chl (Zn) from 90 to 100% -in the area xyzf and α chl (Cu)-in the area nmet.Values of temperature and pressure in boundary points of these technological areas are represented in Table 4.As follows from the data of Table 4, to achieve the 95-100% lead chloride sublimation degree the necessary temperature is 933.7-13000 C and lgP should be from -0.48 to -1.75 (pressure of 0.33-0.0177bar); for achievement of the 90.0-100% chloride sublimation degree for zinc respective parameters are T=1279.3-15000 C and lgP from -0.972 to -2 (pressure of 0.107-0,01 bar), for coppertemperature of 1337.7-15000 C and lgP from -1.418 to -2 (pressure of 0.038-0.01bar).Judging by the table data, at pressure of 0.01 bar the high copper chloride sublimation degree is possible at high temperatures (1337.7 0 C); for zinc it can be lowered to 1279.3 0 C and for leadto 933.7 0 C. At implementation of the sinter-chlorinating roasting of the slags the process temperature should not exceed the slag's melting temperature (1200 0 C 12 ), that is its maximal value may be 1100-1150 0 C.For achievement of high α chl (Zn) and α chl (Cu) values at these temperatures the process pressure should be reduced.
The information about influence of the pressure reduction on α chl (Cu)at the lowered temperatures (1100-1150 0 C) is represented in Table 5.
It is evident, that at temperature of 1150 0 C and pressure of 0.001 bar α chl (Cu) exceeds 85%.At the same time, zinc and lead completely pass in a gaseous condition.The experiments connected with determination of the possibility of application of the distilled liquid for extraction of lead, zinc and copper from the fuming slags T h e ex p e r i m e n t s c o n n e c t e d w i t h determination of the possibility of application of the distilled liquid for extraction of lead, zinc and copper from the fuming slags were carried out on a sintering plant 13 .The charge mass was 300-350 g.Before the sintering roasting the slag and coal (5% of the slag mass) are grinded to the fraction <0.1 mm and pelletized using a solution of the distilled liquid.The granules in diameter of 1-1.2 cm were dried at 200 0 C during 30 minutes.The dry granules were loaded on a fire grate of an agglomeration cylinder (on which we preliminary placed a burnt limestone layer).Ignition of the granules is realized by means of a blowtorch.After the ignition (in 5-8 min) the layer wise burning of the charge with the simultaneous chloride sublimation of the metals occurred.Suction of the gases (including the chloride sublimation gases) is realized with the help of a smoke sucker.Vacuum under the fire-grate was controlled by a manometre.Duringthe ignition periodit was0.006-0.0065bar, and during thechloride sublimation period -0.01-0.015bar.The process duration was 35-40 minutes.Temperature of the material in the layer was 1150-1180 0 C. The metals' chloride sublimation degree was calculated under the formula: Where G (Me(slag) H G (Me(sin) -mass of a metal in a slag and in a sinder after roasting, g.

CONCLUSION
On the ground of the results of the experiments on application of the distilled liquid -the waste of soda manufacture -for extraction of lead, zinc and copper from the dump slags by chloride sublimation it is possible to draw the following conclusions: -at equilibrium conditions lead is extracted the most effectively from the slags by chloride sublimation, then zinc and copper: at pressure of 1 bar and temperature of 1500 0 C the chloride sublimation degree for lead makes 1635.89-164.44•lgP+2.103•T-7.76•(lgP) 2 -6.62•10 -4 •αT 2 +0.0735•lgP•T.1-pressure of 1 bar; 2 -pressure of 0,1 bar The quantitative distribution of the substances containing: a) lead; b) zinc; c) copper Fig. 1.Temperature and pressure effect on the quantitative distribution of the substances containing lead, zinc and copper in a system slag -(CaCl 2 + NaCl) -O 2 1-pressure of 1 bar; 2 -pressure of 0,1 bar Fig. 2. Temperature effect on the chloride sublimation degree of lead, zinc and copper from the slag in the presence of CaCl 2 and NaCl

1 -
the solid representation; 2-the horizontal section Fig. 3. Temperature and pressure effect on the chloride sublimation degree of lead, zinc and copper in a system slag -(CaCl2 + NaCl)-O 2