Abstract
A study of a local industrial symbiosis involving the recovery of platinum from waste thermocouples which is then used for the preparation of catalytic electrodes suitable for dye-sensitized solar cell production is reported. The small quantity of platinum in the filaments of used thermocouples, thousands of which are discarded each year by metal foundries, can be economically recovered by conversion to chloroplatinic acid hydrate, an ‘added value’ product, which can then be used in the fabrication of dye-sensitized solar cell counter-electrodes. 91% recovery of platinum from filaments as chloroplatinic acid hydrate has been achieved by aqua regia digestion of manually isolated filaments. Cost-benefit analysis shows the proposed process derives sufficient value to cover landfill costs for what is left of the waste thermocouples after platinum removal; provide ∼5 days employment; and provide 63% materials cost savings for electrode preparation in comparison to purchasing commercially available chloroplatinic acid hydrate. The proposed local industrial symbiosis would, per year, divert ∼50 g of platinum from landfill, avoid up to 1400 kg of CO2 emissions associated with primary production of an equivalent quantity of platinum, and give enough platinum to produce catalytic electrodes for ∼500 m2 of dye-sensitized solar cells, which could supply clean energy for 12 homes in the locality. The process exemplifies the environmental, economic and social benefits available through adoption of circular practices, which make use of secondary materials available within the local economy by valorizing wastes. The process also overcomes economic barriers to critical raw materials (CRMs) recovery from dissipative applications.
Highlights
The world faces the limits of current ‘linear’ economic models due to resource security issues, growing population and increasing per-capita consumption
It is convenient to discuss the results in terms of: the isolation of filaments from waste thermocouples; the chemical analysis of the chloroplatinic acid hydrate prepared from these filaments and the suitability of this chloroplatinic acid hydrate for dye-sensitized solar cells (DSSCs) electrode manufacture; and the environmental impact, and cost benefit, of the proposed industrial symbiosis
Filaments were snipped as close to their base as possible to minimise the quantity remaining within the refractory cement of waste thermocouples (WTCs) (Fig. 5, stage 1)
Summary
The world faces the limits of current ‘linear’ economic models due to resource security issues, growing population and increasing per-capita consumption. Transition is necessary to a new ‘circular economy’: a resource-efficient industrial economy which decouples economic growth from resource consumption (EC, 2014b; Ellen MacArthur Foundation, 2013; O'Connor et al, 2016). The concept of ‘waste’ is replaced with one of ‘resource’ and process waste is reduced through industrial symbiosis, whereby process waste becomes the feedstock of another process. In this way, materials are retained in an economically productive capacity, cascading across multiple product lifecycles. Enhanced resource-efficiency will deliver synergistic economic, environmental and social benefits (Ellen MacArthur Foundation, 2013). Of significant importance to sustainable economic growth and transition to a low-carbon society is a secure supply of critical raw materials (CRMs),
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