Mining Non-ferrous Metals

A. K. BARBOUR

Introduction

The products of the extractive industries, both metals and minerals, are of pivotal importance to modern life-styles. This situation will continue for the foreseeable future in spite of the inroads made into some non-ferrous applications by plastics, ceramics, and composites. Some of the many applications illustrating this point are indicated in Table 1.

In this introductory review, emphasis is placed primarily on the environmental impacts arising from the mining and concentration of non-ferrous metal ores. Brief reference is made to the efficient management of emissions from non-ferrous smelting processes, recycling, and the environmental issues arising from the significant power requirements of the industries involved.

Unlike organic chemicals and plastics, metals generally cannot be degraded chemically or bacteriologically into simpler constituents, such as carbon dioxide and water, which are relatively neutral environmentally. Metals occur naturally in a wide range of economic concentrations in the ground from approximately 0.05% for uranium, through 0.5–1% for copper, to approximately 60%–70% for iron, and invariably occur in admixture with a wide range of minor and trace metals. Many non-ferrous metals occur naturally as sulfidic compounds. Thus, metals use is essentially metals relocation and requires:

(1) Large energy inputs to extract the ore and to separate the desired metal from undesired mineral substrates and minor metal impurities, i.e. concentration effects.

(2) Consideration of the toxicity of metals and associated impurities, i.e. their chemical type in extraction, purification, and use (i.e. toxicological effects).

(3) Recycling after use or, where this is impracticable, permanent disposal in an environmentally acceptable manner, i.e. collection and process technology issues.

(4) Managing the effects of associated impurities, including associated minor metals and sulfur.

This overall set of processes is summarized in Figure 1.

The production, use, and recycling of non-ferrous metals thus requires a complex series of technologies carried out by organizations of widely varying size and sophistication in many areas of the world exhibiting extremes of climate, development, and political outlook.

2 Environmental Background

The desire to protect the environment from the perceived effects of both the extraction and processing industries is strong in the so-called 'developed world' (e.g. North America, Europe, Japan, Oceania) and growing rapidly in the 'developing' countries, largely through the efforts of various United Nations agencies. Politicians and regulators express these public wishes through increasingly stringent regulations whose true costs are usually impossible to estimate accurately. Slogans such as the 'Polluter Pays Principle' — whereas the consumer usually eventually pays — are sometimes used to suggest that eventually the costs of building new plants to meet modern environmental standards will become so high that such plants will either not be built or will be constructed in 'developing' countries where standards are thought to be lower.

In general, this view is illusory for new construction and largely so for the upgrading of older plants to modern environmental standards provided an adequate time-scale is allowed; say 5–7 years. It is likely that increasing importance will be attached to environmentally acceptable disposal routes for consumer durable and other end-products. This could result in some market restrictions which would find grudging acceptance from producers and consumers of all environmental standpoints.

The non-ferrous metals industry, in common with its product competitors, has also to manage the impact of quite rapidly rising power costs. Technically, these increases are attributed mainly to the cost of developing low-sulfur basic sources of energy and the cost of neutralizing acidic emissions at power stations burning coal of relatively high sulfur content, to minimize 'Acid Rain'. The cost of safely decommissioning time-expired nuclear power stations will also become an increasing factor.

Environmental issues are often presented confrontationally — development or environmental devastation; compliance with criteria versus costs; industry versus the regulators or the 'Greens' — and, indeed, there is never complete congruence between these different viewpoints.

However, the confrontational approach does scant justice to the desires of most people to improve their material standards, not at any cost, but inevitably through industrial activities which provide employment and income as well as products. It also fails to reflect the increasingly general management view that operations must be designed, run, and maintained to the best professional standards, rather than to those which appear to be the most economic in a short-term view.

From a mining and processing standpoint, aspects of implementation of this policy are outlined in the following review. Though mineral extraction, processing, smelting, and refining can never be environmentally neutral, the overall areas of impact are generally quite small. A fully professional approach can achieve a high degree of amelioration provided it is applied consistently and continuously, on a long-term basis, from project initiation to final 'close-out' of the restored and remediated mine and/or refinery.

From the economic standpoint, the cost of meeting inevitably stricter environmental regulations — and the non-regulatory aspects of such disparate issues as accident prevention, including planning for disaster prevention and mitigation, occupational health, product safety, and 'environmental friendliness' in the ultimate end-product — should be judged on a comparative basis, relating one product's total cycle costs to those of its market-place competitors. Whilst the future situation vis-à-vis competition from plastic and composite materials is much more difficult to estimate with any accuracy, it seems likely that non-ferrous metals will retain many, though not all, applications dependent upon electrical conductivity, ease of repetitive manufacture, and the long-term maintenance of essential physical properties such as strength and relative absence of 'creep' and brittleness. The...