<p>The large-scale deployment of negative emission technologies (NETs) is critical for achieving carbon neutrality, but identifying an optimal portfolio that balances economic and environmental sustainability remains a challenge. In this study, a multi-objective model is proposed to identify the optimal NETs portfolio in Northwest China, a region characterized by energy wealth and ecological vulnerability. The developed model aims to simultaneously maximize the economic returns while minimizing environmental footprints, including land, water, energy, nitrogen, and phosphorus consumption. A dual discount rate framework, incorporating both economic and environmental discount rates, is established to analyze the tradeoffs between economy and environment. Results indicate that biochar is the most effective NET and dominates the technology portfolio before 2035. Conversely, bioenergy with carbon capture and storage shows limited effectiveness and sustainability due to its high environmental footprints. In the long term (post-2035), enhanced weathering and direct air carbon capture and storage become essential for achieving deep decarbonization and eventual carbon neutrality. Furthermore, results also reveal that higher economic and environmental discount rates promote the early deployment of NETs but result in a lower economic return and a larger environmental footprint, highlighting a trade-off between short-term action and long-term sustainability. These results provide useful information for formulating optimal NETs deployment strategies and underscore the necessity of incorporating long-term environmental concerns into policy-making to ensure the sustainable achievement of carbon neutrality.</p>