LEAD ZINC

Lead zinc ores generally occur together in such intimate mixtures that they must be mined simultaneously. Clean (PbS) is by far the most important ore mineral of lead. Other commonly occurring minerals are anglesite (PbSO4) and cerussite (PbCO3). The Principal ore of zinc is sphalerite (ZnS). Other important minerals are calamine (ZnCO3) and hemimorphite (2ZnOSiO2H2O). Other zinc minerals include zincite (ZnO) willimite (Zn2SiO4) and franklinite (Fe, Zn, Mn) O (Fe Mn) 2 O3 uni-metal and multimetal deposits also occur.

Lead zinc ores are not directly saleable unless the concentrates of suitable grades are produced. The ores are first concentrated and then malted to produce the metal, which in turn finds a number of applications in various industries. Different flow sheets through floatation techniques are employed to optimize grade and the various in the concentrates from the different types of ores and in this the gangue plays a decisive and vital role. For example the floe sheet and design parameters of the concentrates at the Zawar Group of mines are quite different from Rajpura Dariba, Deri and Ambamata type of ores. The dolomite hosted lead deposit at Sargipalli and Agnigondala leave different designs and flow sheets parameters. Under the circumstances no fixed specifications could be drawn for lead zinc ores. Depending on the type of ore the bench scale and the pilot scale benefaction tests are carried out and appropriate design criteria are evolved to achieve the highest grade and the    recoveries of the concentrates.

In the world generally high-grade lead zinc ores are mined. The Mexican mines run 10 to 13% combined lead zinc with 5 to 6 ounces of silver per tonne. The Canadian mines run about the same, Some Australian producers mine 27% combined lead zinc and about 7 ounces of silver per tonne of ore; other properties in the world run even higher. In U. S. however, comparatively much lower grades ores are exploited, around 4% combine lead and zinc. In Indian for a simple type of lead zinc deposits the average total metal content of over 5% is C considered reasonable under prevailing conditions of technology and economics. However, some complex deposits having high metal content are not viable at present.

The specification of the concentrates for treatment in the 2 lead smelters and 2 zinc smelters of Hindustan Zinc Ltd. Are given below:

1. Tundru Lead Smelters:

Pb       

60 – 62%

Total Sulfur

15 – 17%

Insoluble

2 – 3%

Cu

0.02 – 0.035%

FeO

3.5 – 4.7%

Sb

0.05 – 0.08%

CaO

2.5 – 3.0%

Ag

0.08 – 0.10%

ZnO

5.5 – 7.0%

Moisture

3.5 – 4%

Sol.Al2O3

0.90% 

Bi

Traces

Mg

15 – 17%

Ni

Traces

2. Vizag Lead Smelters:

Pb       

40 – 75%

MgO   

Nil – 2%

SiO2

1 – 9%

Cu

0.005 – 3%

Zn

1 – 5%

Sb

0.02 – 0.7%

Fe

1 – 6%

Bi

Traces – 0.009%

Al2O3

1 – 3%

Ag

0.005 – 0.008%

CaO

Traces

T/S

1.5 – 18%

3. Debari Zinc Smelters:

Zn

50%

Cu

0.1%

Sulfer

31%

Cd

0.3%

Fe

7%

Fluorine

Traces

Pb

1.5%

H2O

5 - 10% (max.)

4. Vizag Zinc Smelters:

Zn

52% min.

Mg

0.25% Av.

Cd

0.25% Av.

As

0.10% Av.

Pb

2.5% max.

Co

0.002% max.

Fe

8.5% max.

Ni

0.002% max.

Cu

0.8% max.

Tin

0.004% max.

CaO

2.5% Av.

MgO

2.80% Av.

Cl

0.06% max.

Al2O3

1.00 Av.

E

0.01% max.

S

29.0%

Ge

29.0%

Sb

0.035% max.

SiO2    

1.00%

   

In the case of lead zinc ores cut off grades and the average grade are important. Formerly detailed information regarding cut-off grade, average grade, mill head grade, etc. was not available. But now HZL has supplied information about these parameters, and as a result it has been possible to break up the into "reserves" and "conditional resources" taking in to consideration the cut-off and the averages grade as given below:

i

Reserves

Pb + Zn

(+) 5% average
(+) 3% Cut-off

ii

Conditional resources

lower than the above grade.

 

As discussed above the viability of a deposit is governed by a number of factors. The lower price of zinc has been a limiting factor in the exploitation of lower grade deposits. Co-production and by-production of associated metal is a very common feature in lead zinc industry. Total in Indian certain higher-grade deposits are not commercially viable. Minimum lead and zinc content in a deposit should be 5%. Accordingly the following classification is suggested for the guidance of geologist.

i

Reserves

Pb + Zn

5% and above (average)
2 – 3% min. (min. cut-off)

ii

Conditional resources

Pb: Zn (-)

5% (average)

iii

Associated metals

 

Specify grades

iv

Gangue

 

Specify


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