Zinc solubility

A remedy could be achieved by a decrease in the zinc solubility in the electrolyte or by suppression of dendrite formation cadmium-, lead-, or bismuth oxide,... 

Concentrations of free Zn in soil solution are strongly dependent upon soil pH. Zinc solubility expressed as free Zn increases with the concentration of LL (Norvel and Lindsay, 1969 Dang et al., 1994 Tiller, 1983 Jeffery and Uren, 1983). Norvel and Lindsay (1969) proposed that the solubility of soil Zn could be described by the equation ... 

The separators may be simple absorbent material except in Ni/Zn where zinc solubility creates zinc electrode shape change and zinc dendrites, resulting... 

Corneau, L., Lavigne, C., and Zee, J. A. (1996). Effect of calcium and zinc concentrations and calcium source on in vitro calcium and zinc solubility in a fiber-fortified enteral formula. Nutr. Res. 16,1659-1669. 

PHYSICAL PROPERTIES silvery-metallic, lustrous solid darkens on exposure to light forms hexagonal close-packed crystals brittle much harder than zinc soluble in dilute acids and potassium hydroxide solution odorless MP (1522°C, 2772°F) BP (3338°C, 6040°F) DN (4.469 g/cm ) SG (4.47) CP (26.5 J/K-mol crystal at 25°C) VD (NA) VP (0 mmHg at 20°C). 

The bioavailability of zinc is higher in media with a low pH, as a result of increased zinc solubility and ionization. If zinc is partly present in an irreversibly adsorbed state in soil, this part is not available for skin absorption. It would be useful to develop quantitative data on the bioavailability of zinc from various environmental media. 

Saeed M, Fox RL. 1977. Relations between suspension pH and zinc solubility in acid and calcareous soils. Soil Sci 124 199-204. 

Carrying out the extraction process in an enclosed vessel (test 5) to prevent the loss of free CO2 in the pH 7 test solution, produced a statistically significant increase in the amount of zinc extracted (Table 4.4d). In open beakers, the pH increases (up to about 8) during the 24-hour period because of the loss of free CO2, whereas this phenomenon does not occur in enclosed vessel where the pH remains lower. As zinc solubility decreases when pH increases, the differences between test 1 (open beakers) and test 5 (enclosed vessel) are consistent with the theory. Unfortunately, the results from the two laboratories concerned, Kiwa and TZW, were not in the same statistical populations. Slight differences in start pH (tolerance in BS 7766 is 7.0 0.2) could explain this difference. 

An azns=0.05 to 0.1 corresponds to a 1-2 wt% zinc solubility in the matte because the activity coefficient, yzns >n the matte is about 10 as moitioned earlier. Because the Zn solubility in a Fe-S-0 matte is very low under these conditions, the matte can be considered a Fe-S-0 temaiy system whose composition is defined at a fixed temperature, oxygen potential and sulfur potential. Based on the reported relationship between the Fe-S-0 matte composition, temperature, oxygen and sulhir potentials (2), Fe-S-0 matte compositions under the described smelting conditions have been estimated see Table I. At 1350°C and a CO/CO2 ratio between 3 and 4, azns=0.05 (or less than 1% Zn solubility in matte) requires the composition of matte of 6-7% O and Fe/S 2.7-2.9 (weight basis). The proposed matte smelting composition is shown in Figure 2 (6). 

Zinc solubility in the matte as a function of the process parameters... 

The zinc solubility in the matte is affected by the partial pressure of zinc and the temperature under a given matte composition. To compare the zinc solubility from one test to anodier, this must be normalized to a standard zinc partial pressure, say 0.1 atm, and a temperature. The normalized zinc solubility at 0.1 atm zinc partial pressure was calculated by dividing the measured zinc solubility by the corresponding zinc partial pressure and by 10, (Zn wt%) / (10 Pzi,). As discussed in the above section, an increase of SO C in temperature causes a 40-60% decrease in zinc solubility for a given matte composition. Thus, the normalized zinc solubility at Pzn= 0.1 atm and experimental temperature was converted to that at 13S0°C by considering the effect of temperature. These zinc solubility data is summarized in Table IV as normalized zinc solubility at Pzn = 0.1 atm and 1350"C. 

Table IV shows the results of the tests in detail. Test-1 was done in two different temperature ranges, 1250-1300°C for the first 30 minutes and 1400-1430°C for the second half of the test. The zinc content in the Fe-S-0 matte increased as the test proceeded, until at 30 minutes, it reached its maximum, 1.37 wt%, which is considered the saturation value. In the second half of the test, temperature was increased to 1410-1430 C and the zinc solubility decreased to -0.5 wt% which basically is the same as that present in the feed. It is worth noting that the zinc concentration in the matte before the test should be very small because there was no zinc added to the system at the begiiming. The reported value might be due to a chemical analysis error. If this were true, the zinc recovery into the gas phase was almost 100% for the second half of the test at a temperature >1400°C. Figure 8 shows the changes in zinc solubility during the test.

The present test was done at Pzn= 0.34 atm. It is expected that zinc solubility in the Fe-S-0 matte would be even lower if the zinc partial pressure was controlled at 0.1 atm. 

Test 1 successfully demonstrated the feasibility of the process to use metallic iron to fix sulfur. This test indicates that the activity coefficient of ZnS in matte is very large because the zinc solubility is about 1 wt% even at Pa = 0.34 atm and 1350 C, whereas the normalized zinc solubility in the matte is only 0.24 wt%. 

This test was designed to examine the feasibility of sulfur fixation using iron ore instead of metallic iron and to find the equilibrium zinc solubility in Fe-S-O matte. Therefore, this test was carried out under a high gas flow rate and with a low solid material feed rate. Initial matte preparation was done exactly as in the previous test. The molten bath temperature was controlled to around 1350 °C. A solid mixture with 44% zinc concentrate, 48% iron ore and 8% charcoal was injected into the bath at a feed rate of 19.5 g/min with 20 NL/min nitrogen carrier gas to give Pzn = 0.066 atm. 

The solubility of zinc is much higher than in the previous tests because of the lower Fe/S ratio. This agrees with the theoretical analysis. Zinc solubility is proportional to the square root of the sulfur potential, whereas the sulfur potential is controlled by the Fe/S ratio the higho the Fe/S ratio, the lower the sulfur potential. Nevertheless, the "normalized solubility of zinc in matte at Pzn = 0.1 atm is less than 2 %wt even at a Fe/S ratio of 2.22. 

This test was designed to examine the effect of the partial pressure of Zn on the solubility of zinc in the matte. Nitrogen flow rates were changed fixtm 8 NL/min to 12 NL/min under otherwise identical experimental conditions. It was found that the solubility of zinc in the matte decreased with increasing nitrogen flow rate. However, the normalized zinc solubility in the matte remained constant (within experimental error). This is in agreement with theory, indicating that the solubility of zinc in the matte is in equilibrium with the zinc-laden gas. 

Test-7 was done at CO/CO2M. The average matte composition is Fe/S=3.77 and 6.51% O. The zinc solubility is lower than that in Test-6 because of the lower oxygen content of the matte or the lower oxygen potential. 

Figure 9 summarizes the influence of the oxygen content on the zinc solubility for Tests-5, 6 and 7 having a Fe/S ratio between 3.3-3.7. It is seen that the solubility of zinc is directly proportional to the oxygen content of the matte. 

Figure 9 - Effect of Oxygen on the Zinc Solubility in the Matte...

Test-10 was done to demonstrate the technical feasibility of volatilizing zinc by feeding zinc oxide into a pre-melted Fe-S-O matte. A solid mixture consisting of 81% ZnO and 19% charcoal was injected into the bath at a feed rate of 50 g/min by air. The zinc solubility of the matte was about 0.9 wt% Zn at Pzn=0-1 atm and 1350°C. This test successfiilly demonstrated the feasibility of treating zinc oxide materials in the Fe-S-O matte by using carbon as a reductant and oxygen as the diluting gas. 

Table V summarizes the experimental results of the tests with low oxygen content in the matte i.e., tests 1-5,9and 10. The matte conqxrsititMi and nramalized zinc solubility at Pzn=0.1 atm and 1350°C as reported Table III are repeated here. The zinc solubility has been converted into mole fractions to calculate the activity coefficient. The sulfur potentials at 1450 and 1200°C are taken from the reported activity diagrams for Fe-S-O matte (9), from which the sulfur potentials at 1350°C are estimated. The activities of ZnS in the matte were calculated from azns = K Pzn (Ps2), where K is the equilibrium constant for reaction Zn(g)+V2S2(g)=ZnS(l) and was estimated to be 64 at 1350 C. The activity coefficient of ZnS in the matte was estimated (Table IV). Although the estimated activity coefficient of ZnS varied from 7 to 22, it has an average value of 12.6 and is very close to the reported value, 10 (8). Considering the many possible sources of aror in the tests, it is not surprising that there is a large scatta in the estimated ZnS activity coefficient Nevertheless, the experimental data wae in close agreement with the theoretical predictions.

Figure 10 shows the zinc solubility obtained experimentally as a function of the Fe/S ratio. The zinc solubility decreases with increasing Fe/S at the lower Fe/S ratios. The scatter in the lower zinc solubility range is large. This might be attributable to analytical errors, because even for the initial "blank" Fe-S-O matte, the analytical results vary from 0.05 wt% Zn to 1.0 wt% Zn. 

Figure 10 - Measured Zinc Solubility as a Fimction of the Fe/S Ratio in Matte...

The capacity for imdesirable elements at Big River Zinc falls into two categories. The first category involves elements such as sodium and potassium. These elements do not affect the equipment and they do not directly affect the process. The problem with these elements is that the process used at Big River Zinc does not eliminate them. As a result, they build up in the electrolyte resulting in a lower zinc solubility. This increases the production cost because of the need to treat more solution to produce the same quantity of zinc. 

Recent development work has extended the cycle life of nickel-zinc batteries through the use of additives in the negative electrode in conjunction with the use of a reduced concentration of KOH to repress zinc solubility in the electrolyte. Both of these modifications have extended the cycle life of this system so that it is now being marketed for use in electric bicycles, scooters and trolling motors in the United States and Asia. 

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