Lead & Zinc - Mine To Metal

Introduction

1. It is one of the most important of base metals, that constitute one of the most essential requirements of industrial development of a country. Lead-Zinc both being chalcophile element, geological conditions favour the formation of lead and zinc together. Therefore, both lead and zinc are found to occur together with other metals (copper, gold, silver) forming polymetallic base metal deposits i.e., lead and zinc deposits with variable ratio of these metals.
2.  Galena (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), Hemimorphite (2ZnO SiO2-H2O), Zincite (ZnO), Willemite (Zn2SiO4) and Franklinite (FeZnMn)(FeMn)2O3.

In chemistry, the term base metal is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with diluted hydrochloric acid (HCl) to release hydrogen. In mining and economics, base metals refer to Industrial non-ferrous metals excluding precious metals. These include copper, lead, nickel and zinc.

Resources

1. The total Indian resources of lead and zinc ores as on 1.4.2010, as per UNFC system, are estimated at 685.59 million tons. Of these, 108.98 million tons (16%) fall under ‘reserves’ while the balance 576.61million tons (84%) are classified as ‘remaining resources’. The resources of ore containing +10% Pb & Zn were estimated at 139.85 million tons, ore containing 5 to 10% Pb & Zn were 252.30 million tons and ore containing less than 5% Pb & Zn were estimated at 293.44 million tons.
2. Rajasthan is endowed with the largest resources of lead-zinc ore amounting to 607.53 million tons (88.61%), followed by Andhra Pradesh 22.69 million tons (3.31%), Madhya Pradesh 14.84 million tons (2.16%), Bihar 11.43 million tons (1.67%) and Maharashtra 9.27 million tons (1.35%). Resources are also established in Gujarat, Meghalaya, Odisha, Sikkim, Tamil Nadu, Uttarakhand and West Bengal.
3. Lead and Zinc occurrences (over 88%) are located principally in Rajasthan (Udaipur, Rajsamnd, Bhilwara, Ajmer, Chittorgarh, Pali and Sirohi districts). In addition occurrences of lead – zinc have also been located in Andhra Pradesh (Cuddapah, Guntur and Prakasam districts), Bihar (Banka and Rohtas districts), Gujarat (Bansakantha and Vadodara districts), Madhya Pradesh (Betul district), Maharashtra (Nagpur district), Meghalaya (East Khasi district), Odisha (Sundargarh district), Sikkim (East Sikkim district), Tamil Nadu (Villupuram district) and Uttarakhand (Dehradun and Pithoragarh districts).
4. In India, Lead & Zinc ores are exploited basically for recovery of respective metal by smelting. The Lead & Zinc content in sulphide ores is invariably too low to meet the stipulation of smelter, therefore, it is necessary to beneficiate Lead-Zinc ores to produce smelter grade concentrate. Flotation is the only route practiced in the country to produce a smelter grade concentrate.

Lead and Zinc Ores are the largest sources of silver and cadmium. Silver is closely associated with the galena while cadmium is with sphalerite and constituted an important by-product.

Need For Processing

Lead and Zinc ores are exploited basically for recovery of respective metal by smelting. These ore because of its low tenor/content, in run-of-mine ores must be concentrated before smelting and refining. Beneficiation, which usually occurs near the mine site, consists of crushing, grinding, and flotation to produce concentrates of 50 to 60 percent lead & zinc.

The objectives for beneficiation of lead and zinc ores are:

i) The recovery of smelter grade lead and zinc concentrates with maximum lead and zinc distribution with minimum contamination/ misplacement.

ii) Recovery of separate concentrate of other associated minerals with minimum contamination/ misplacement, and

iii)  Recovery of precious metals, which are generally recovered during lead and zinc electro-refining. 

Process of Beneficiation of Lead and Zinc Ore

The flotation route of beneficiation is the most appropriate and widely accepted process for lead-zinc ore in the country. The process route encompasses Feed preparation, Concentration and Dewatering sections and is discussed herewith.

Feed preparation Section:

1. CRUSHING: ROM ORE (1000 mm) -------Multistage Crushing (Primary - Jaw /Gyratory) --–100-200 mm, secondary (Cone & Roll) ----- 20-50 mm & tertiary (short head Cone crusher) ------- 10-20 mm

2.  GRINDING: Rod mill ----------10 mm -------Ball mill---------Classifier ------ overflow to flotation circuit.

Concentration/flotation Section:

Feed from Grinding-classification circuit i.e., Overflow -------

1)     Selective Lead-Zinc flotation

2)    Bulk Lead-Zinc flotation

Dewatering & Tailings Disposal

Hindustan Zinc Limited (HZL)

M/s Hindustan Zinc Ltd (HZL), a former Government of India Undertaking, is involved in mining, beneficiation, smelting, and marketing of zinc, lead and its by-product in India. HZL is the leading lead-zinc producing company in India, which has several lead-zinc mines and smelters. It is a Vedanta Group company in Zinc, Lead and Silver business. It is the world's largest integrated producer of Zinc-Lead and also leading silver producers in the world. Principal products are: refined Zinc metal and refined Lead metal. In addition, they also recover Silver, Cadmium and Sulphuric acid. They are one of the lowest cost producers in the world and are well placed to serve the growing demand of Asian countries. Hindustan Zinc is a subsidiary of the Sterlite Industries (India) Limited. HZL has lead production capacity of 1,85,000 tpy and zinc production capacity of 8,79,000 tpy.

Disclaimer: The views expressed are personal and after interactions with Industry Experts

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