RESUMO
Economic value is no longer adequate by itself as a proxy for the value-added benefits (VAB) assumed to be generated by emerging technologies such as engineered nanomaterials (ENMs). This study was conducted to explore the potential to establish an integrated sociotechnical framework with the end goal to assess whether or not ENMs and nano-enabled products contribute VAB. Based on the research in this study, it is suggested that all stakeholders in the larger society-environment-economy (SEE) system should develop an understanding of the multiple interrelationships within and between the diverse constituents along the particle lifecycle trajectory to capture their influence on the system benefit and risk outcomes. Furthermore, the sociotechnical framework establishes an additional three-step process: (1) at the pre-design stage, the test of VAB should be assessed using an expert panel representing the different segments of SEE, the social principles of design are detailed and customized to the needs of ENMs and nano-enabled products, and an economic appraisal is conducted to justify the VAB on material grounds; (2) at the design stage, the technical principles should be examined and detailed to ensure the compatibility of stakeholder needs; and (3) an iterative adaptive cycle should be conducted to re-examine the sociotechnical principles on a periodic basis. Within this context, ENMs are considered sustainable when (a) the conditions of VAB and minimal risk elements are satisfied in a sequential order, with VAB demonstrated at the pre-design stage, then at the design stage ENMs posing no harm greater than minimal levels to the SEE constituents; and (b) ENMs and nano-enabled products are bounded by a finite time limit. In addition, to reach the conditions of sustainability, the role of all SEE stakeholders should be broadened (e.g., regulatory agencies should transform their roles from not only the control of risks of negative implications, but also the establishment of positive implications as well).
RESUMO
Salt cake is a major waste component generated from the recycling of secondary aluminum processing (SAP) waste. Worldwide, the aluminum industry produces nearly 5 million tons of waste annually and the end-of-life management of these wastes is becoming a challenge in the U.S. and elsewhere. In this study, the mineral phases, metal content and metal leachability of 39 SAP waste salt cake samples collected from 10 different facilities across the U.S. were determined. The results showed that aluminum (Al), aluminum oxide, aluminum nitride and its oxides, spinel and elpasolite are the dominant aluminum mineral phases in salt cake. The average total Al content was 14% (w/w). The overall percentage of the total leachable Al in salt cake was 0.6% with approximately 80% of the samples leaching at a level less than 1% of the total aluminum content. The extracted trace metal concentrations in deionized water were relatively low (µgL(-1) level). The toxicity characteristic leaching procedure (TCLP) was employed to further evaluate leachability and the results indicated that the leached concentrations of toxic metals from salt cake were much lower than the EPA toxicity limit set by USEPA.
