Figure 1. Map of the nine STAF regions.

This paper characterizes the anthropogenic life cycle of silver for 1998 in the Commonwealth of Independent States (CIS) of Central Asia, one of nine world regions designated by the STAF group (Figure 1). Research has been completed and published for both the global copper and global zinc cycles (Lifset et al. 2002, Gordon et al. 2002), while data analysis for the regional silver cycles is currently in progress. Recognizing the limitations of data availability and accuracy, the STAF group aims to capture a minimum of 80% of all significant flows of silver. Four countries from the CIS were selected to represent the majority of flows – Kazakhstan, Russia, Ukraine, and Uzbekistan, which together make up 93% of the regional silver production (CPM Group 2001) and 81% of the population of the CIS (World Bank 1997, CIA 2002).

Country-level data have been collected and used to produce a regional-scale model of the flows and stocks of silver for this one-year time scale. The resulting cycle can be used to assess the magnitude of silver usage, the role of international precious metal trade, the extent and nature of silver waste leaving CIS economies, and the sources of dissipation. In turn, this information can be a key component for the establishment of environmental regulations, reserve estimation, and energy policies.

Figure 2 . STAF system boundary diagram. Arrows represent the direction of silver flow. (Click to view enlarged image)

Production

          Production was divided into three sub-processes:

(a)Mining, milling and flotation: Silver ore is mined and purified to produce concentrate for refining. Waste tailings are also produced and are returned to the environment (Hilliard 2001). Mining may be from primary ores (containing mostly silver) or from base-metal ores (lead/zinc or copper ores with small silver concentrations).

(b)Separation processes: It was calculated that in the CIS, smelting of ores is used for approximately 79% of silver ore processing (Table 2). Smelters produce silver concentrate, but release waste containing silver, known as slag, which may be recycled or lost to the environment. Cyanide leaching is also used to purify an estimated 16% of ores, and cyanide wastes containing trace silver can be released to the environment. Other processes, such as thiosulfate leaching (Renner et al. 2002) account for approximately 5% of processing.

(c) Refining: Silver concentrate is further processed to produce refined silver that may be exported or used for fabrication within the country. Old scrap (Table 1) may also be recycled and used in the refining process.

F & M

In order to calculate the trade of silver in these products, statistics were used from the U.N. Comtrade database for imports and exports of various products. The weights of these products, when available, were used directly to calculate the flows into and out of F&M. When no weight data for a country were available, a conversion factor was used to translate the monetary value into weight, based on an average of other countries that reported both monetary and weight data. Each of these products had an estimated silver concentration that was used to calculate the net trade flows of silver. For countries that did not report data, such as Ukraine and Uzbekistan, the trade flows were inferred based on other countries’ reporting. A waste flow from the manufacturing of circuit boards was also calculated (Table 3), and a closure balance was incorporated to account for any silver not included in known flows.

Use

Silver entering into use includes the sum of silver derived from CIS-manufactured products and from imported products. Recycling of products occurs in both the F&M stage and the use stage. In F&M, scrap may be recycled internally or returned to the refining process in production. Recycling flows from use are assumed to be from on-site recycling of photographic waste, which is estimated for more developed countries (Table 3). For the CIS, this statistic was modified based on the relative GDP, assuming that less-developed countries would use a smaller amount of photographic materials. The amount of silver entering stock was calculated by the difference between the usage (Figure 3) and the flow into waste.

Figure 3 . Silver entering use by sector in CIS region. Other industrial applications include dental amalgams, mirror coatings, industrial catalysts, and bactericides/algaecides in water purification systems.

WM

WM data for CIS countries were unavailable in many cases, so estimations based on European statistics were often employed. Wastes from the use and F&M stages may enter the environment directly or undergo treatment before release. Approximately 84% of silver waste from use enters the WM stage via five flows that are sent to treatment:

(a)Municipal Solid Waste (MSW): This is waste generated by households, shops, markets, offices, and open areas (UN ESCAP 2000) that contains silver from discarded photographic prints, dental fillings, coins, silverware, etc. The MSW generation per capita and metal content of waste (UNECE 1999) was used to estimate the amount of silver discarded in each country (Table 3).

(b)Sewage and Sewage Sludge (SS): Silver waste from sewage is due to photographical developing waste, medical sewage, domestic sewage water, electroplating work, etc. There were no available data for CIS sewage sludge generation. Therefore, it was estimated for CIS countries based on scaling with European countries, knowing the percentage of the public connected to wastewater treatment plants in the CIS (World Bank 1998, UNECE 1999).

(c) Waste from Electronics and Electrical Equipment (WEEE): This category consists of silver from the circuit boards of discarded appliances, which contain approximately 0.2% silver by weight (Siemers and Vest 1999). This waste stream also contains silver waste from the fabrication of circuit boards, as stated above.

(d)Industrial Waste (IW): Industrial waste is taken as wastes from photographic processing, of which 45% are discarded as waste (Ressourcen Management Agentur 2000).

(e)Hazardous Waste (HW): This category combines waste from silver-oxide batteries and dental amalgam. For the CIS, no data were available for these specific categories. As a result, battery waste was estimated using German data (Vest and Jantsch 1999) that were scaled down based on both GDP and on the ratio of urban population. Data on dental amalgam waste was obtained from a California study (Barron 2001) that estimated the silver waste from dental amalgams as a percentage of silver products entering waste, together with the ratio of this waste entering the hazardous waste stream.

Figure 4 . Silver entering use by sector in CIS region. Other industrial applications include dental amalgams, mirror coatings, industrial catalysts, and bactericides/algaecides in water purification systems.

The flows entering waste management (Figure 4) were directed into numerous processes. A percentage of the flows was incinerated and then landfilled, or directly landfilled. Another portion of waste was recycled as scrap (GFMS 2002) and the remaining waste entered the environment directly, via losses from the wastewater treatment plant, open dumping, or use of sewage sludge in agriculture. Waste from silver in untreated sewage was also directed to the environment (European Environment Agency 2003). Rates of recycling, landfilling, and agricultural usage were estimated based on data from the UNECE Environmental Performance Reviews for CIS countries. A closure balance was again used to account for inaccuracies in data.

Figure 5 Silver cycle for CIS, 1998. (Click to view enlarged image)

Of the 1,140 tons of refined silver used in F&M, 780 tons come directly from the mining sector and recycling of scrap, while an estimated 360 tons are used from stock. This stock was calculated as a closure balance and may be due to the usage of government silver stockpiles in Russia. The World Silver Survey 1999 theorizes that the disposal of stocks in Russia in 1998 may have been motivated by high silver prices as "an emergency measure implemented by a cash-strapped government" (GFMS 1999). Only 8% of manufactured silver left the CIS as net silver product exports, while 86% entered the use stage.

A total of 980 tons of silver entered use, but 54% of this became discards in municipal solid waste, sewage, hazardous waste. etc., while 46% entered existing silver stock. For the WM phase, a closure balance of 220 tons was needed to account for the total 750 tons of discarded silver entering this stage. Roughly 530 tons of silver were discarded directly from manufacturing processes and from use. Of this total waste silver, 48% was recycled as scrap and 52% returned to the environment either through landfilling or through dissipative losses to the environment.

As a whole, the silver returned to the environment is almost 50% of the total silver mined in the CIS. Of this silver, 35% is contained in landfills that are estimated to retain almost 320 tons of discarded silver. Mine tailings are also a major depository of silver, with 370 tons of waste silver or 41% of the environment reservoir as defined by STAF.

Figure 6 Silver flows per capita for Uzbekistan, 1998 (g/capita per annum).

Data Accuracy

The countries of the CIS are still considered to be in the transition stage after the break-up of the former Soviet Union, with continuously changing political, economic, and social climates. As a result of reorganization and shifting control in policies and management, data were often unreliable, inconsistent, or simply unavailable in many cases (Task Force for the Implementation of the EAP 2003). Even agencies outside the CIS, such as the British Geological Survey, the U.S. Geological Survey, and the Silver Institute, were forced to use estimates, as was clearly evident from the wide variation in statistics on this region. Political influence may also have played a role in data release about sources of silver such as government stockpiles. It was especially challenging to locate waste management data due to obsolete or inoperative reporting systems, leading to the use of estimation based on other regions. Despite these uncertainties, the results illustrate a fair representation of the characteristic flows and stocks of silver in the contemporary CIS environment. 

Environmental Implications

Silver metal and its compounds, such as silver nitrate and silver oxide, can be considered toxic or hazardous when discarded or dissipated. The methods used in the mining, fabrication, and disposal of silver often create environmental threats, such as land degradation and water contamination. Tailings from the mining of metals are typically left to accumulate in heaps, often without proper partitioning from the outside environment. The U.N. Economic Commission for Europe reports that 5.1 billion tons of tailings from the mining and enrichment of non-ferrous metals have accumulated on 14,000 hectares of land in Kazakhstan alone. Large areas have been damaged environmentally as a result of inefficient mining operations and inadequate tailings management. Cyanide that is used in separation processes is a toxic chemical and may be a source of contamination when released directly to the environment. If cyanide wastes from silver ore processing enter the ecosystem via leakages or improper disposal, water quality and human health can be compromised.

Waste disposal and management are also potential sources of environmental concern. Discards of silver oxide batteries and dental amalgam (containing mercury) are classified as hazardous waste, but may often enter the environment as a result of unsuitable disposal or lack of recycling. Landfilling or open dumping of waste creates landscape degradation, especially if landfills are improperly managed and filled beyond capacity, as is the case in many CIS countries. Releases of silver from both sewage sludge and untreated sewage can cause contamination of soils (Agency for Toxic Substances and Disease Registry 1990).

In order to assess these environmental implications, it is necessary to quantify the volume of flows of materials between reservoirs. The silver cycle presented above can be used to analyze, for instance, the amount of tailings and separation wastes generated in the production phase, the losses of silver to the environment via unrecorded disposal methods, and the potential sources of contamination. By investigating the flow of silver in the CIS economy, one can minimize environmental impacts by identifying significant negative aspects. For example, a shift in production methods away from cyanidation (such as has occurred in Europe) would result in less potential for contamination. Proper management of landfills would ensure minimal ecological consequences and suitable leachate control. Adequate disposal or recycling of photographic waste and batteries would decrease waste and supply alternate sources of silver. 

Policy Implications

Analysis of the silver cycle and its environmental implications can lead to the development of policies dealing with resource availability and reuse, waste management, processing efficiency, recycling, and trade initiatives, to name a few. Silver consumption has exceeded ore extraction since 1951 (Agency for Toxic Substances and Disease Registry 1990, GFMS 2002), so that secondary production of silver from scrap has become necessary to keep up with rising demands. If this trend continues, worldwide demand for silver could exceed the available supply. By examining the silver flows in the CIS, one can determine the potential for silver recovery and secondary production.

Mine tailings and landfills are the largest depositories of silver waste, containing 76% of the silver discarded to the environment in the CIS. In Uzbekistan, there are many tailings and waste heaps from obsolete mining operations that have been simply abandoned due to inadequate policies of environmental rehabilitation (UNECE 2003). Almost 30% of silver mined is left as waste, in tailings and slag from processing. These waste heaps could provide valuable sources of secondary silver through reprocessing using more efficient methods of recovery, an especially intriguing prospect for mining companies looking to reduce waste and increase outputs.

Silver is also dissipated through sewage wastes, photographic wastes, and lack of recycling. Policy implementation could increase the percentage of the population connected to wastewater treatment plants, effectively capturing more discarded silver before it is released to the environment. In Russia, only 55% of the population is connected to public wastewater treatment plants. A mere 3% of Russian municipal waste undergoes some form of post-collection recycling, composting, or incineration (OECD 1999, Zamparutti 1999). Recycling programs (such as for photographic disposals) on a national level would lead to greater recovery of silver, as well as reduced generation of waste. Facilities for waste incineration would also reduce the volume of waste, although this method of disposal may not be cost-effective in all areas (UN ESCAP, 2000). Municipal separation and collection of silver oxide batteries for recycling could also be implemented, especially as these batteries have economic value.