**1. Introduction**

As nations undergo a low-carbon energy transition, including large-scale electrification and a shift toward a more e fficient transportation system, the need for mineral raw materials (ore and concentrates), some of which are critical, are expected to increase [1,2]. Japan is a nation which is highly dependent on the import of such raw materials for industry, and the need to conserve limited resources and maintaining resource security are considered important to the Japanese public [3]. Japan is completely dependent on imports of raw materials such as for ferrous and non-ferrous metal ores and concentrates (e.g., iron, copper, lead and zinc), which makes it vulnerable to potential global supply disruptions. Such disruptions may occur for various political, economic and environmental reasons. Recent discourse around resource security has been focused on critical materials, essential for industry, civil life and military applications for which alternative materials are not available and which use minerals whose probability of supply restriction is elevated or, in some cases, whose environmental implications of supply are high [4]. "Critical materials" can be broadly defined as relating to materials that fulfil an important (or vital) role in society and for which there is a high possibility of supply restriction, which could lead to higher prices (economic scarcity) or physical unavailability (physical scarcity). A variety of factors are typically included in the evaluation of "criticality", which includes factors of economic importance or reliance (vulnerability to supply restriction, including the number of people using, the importance to economic sectors and the potential for substitution) and supply risk (factors that a ffect this might include the level of monopolization of supply chains, environmental intensity of production and governance in producing countries). Taking copper for example, it is vital to some applications such as electric wire but can be substituted with aluminum with some loss of performance; at the same time, the global production of copper ore is quite diversified, giving a potentially lower supply risk. Due to increasing demand and potential for lagging supply, ore grade decline in terrestrial mines and potential subsequent cost increases per ton of metal, it may face both economic and physical scarcity.

The specific definition of a critical material di ffers from nation to nation, depending on the applied evaluation criteria although materials such as rare earth elements (REE) and Platinum group metals (PGM) are common among materials considered as critical in most nations. In Japan, as a country that is almost entirely dependent on imports of raw materials, apart from the concept of "criticality", other metals are considered "strategic" due to their economic importance (regardless of the likelihood of global supply disruptions which is included in criticality), including copper, lead, nickel and zinc [5–7]. This reasoning underpins their consideration as strategic materials in Japan.

Resource importing countries have severe limits on their ability to exert control over political, economic or environmental issues which are occurring in resource exporting countries. Cognizant of this limitation and, as metals play an important role in achieving a low-carbon society [8], many import-reliant countries have seen the need to develop a resource acquisition or resource security strategy. Application of these strategic metals to renewable energy includes, for example, photovoltaic panel requiring copper, indium, gallium and selenium and wind turbines requiring nickel, molybdenum, neodymium and boron as functional materials [8]. As renewable energy installation increases, battery demand will also likely increase. Lithium-ion batteries are one key storage option in renewable energy societies, and these also include potentially critical minerals such as cobalt and lithium [8]. In order to improve low levels of raw-material self-su fficiency, each country needs to decide their own approach. For example, the USA drew up the Critical Materials Strategy [7], the EU developed the Critical raw materials for the EU [5], while the Japanese governmen<sup>t</sup> outlined their strategy in the Strategic Energy Plan [9]. This plan includes a raft of measures, such as, supply diversification, recycling of end-of-life products and research and development for extraction from unestablished or alternative materials [6]. Of these measures, all are dependent on other nations, except for research and development and domestic recycling of end-of-life products. In order to ameliorate this issue, domestic mineral production needs to be considered alongside domestic recycling in order to achieve resource security, critical to the low-carbon energy transition. The circular economy is one tightly-linked concept to maximize resource e fficiency and minimize waste production, within the context of sustainable economic and social development [10]. Promoting recycling is one of the key components of the circular economy, as well as a key strategy for critical material resource security.

This research focuses on the e ffects of domestic copper production and recycling in Japan. Copper is selected from among the group of critical materials as it has many applications and demand is expected to increase due to expanded renewable energy deployment such as CIGS photovoltaic panel and CIS (copper (C), indium (I) and selenium (S)) photovoltaic panel [11]. Recently, the United States published a federal strategy, which focuses on the improvement of critical mineral supply by: Identifying new sources of critical minerals, enhancing activity at all levels of the supply chain, seeking to stimulate private sector investment and growth of domestic downstream value-added processing and manufacturing, ensuring that miners, producers, and land managers have access to the most advanced mapping data; and outlining a path to streamline leasing and permitting processes in a safe and environmentally responsible manner [12]. Resource acquisition options for an import-reliant country include (1) on-land mining, (2) imports of raw materials, (3) recycling, and (4) unconventional resource exploration. In the context of Japan, because of its lack of on-land mines, option (1) is unlikely. In terms of improving resource security, option (2) does not relieve the vulnerability to export restrictions by exporting countries. Lacking known deposits on land or near shore, development of domestic primary production is focused on ore production by means of deep ocean seafloor massive sulfide (SMS) mining. Thus, recycling and deep sea mining (which is a subset of option (4)) are the options to be discussed in this study.

This study aims to assess the constraints of energy, material, economic and labor under domestic mineral production.
