Corrosion is a significant problem in many industries, and when using stainless steel, passivation is undertaken to improve corrosion resistance. Traditionally, nitric acid is used within the passivation step; however, this has some detrimental environmental and human health impacts during its production and use. Reducing this impact is critical, and because of its toxicity and associated occupational risk and special disposal requirements, end users of passivated stainless steels are exploring alternative passivation methods. However, it is also critical to understand the impact of any alternatives. Sustainable processing and manufacture embodies many elements, including waste reduction, resource efficiency measures, energy reduction, and the application of ‘green’ or renewable chemicals. To ensure the most effective system is used, the impact or potential impact of the system must be measured and options must be compared. The comparative environmental credentials of bio-based chemicals can be assessed using tools such as life cycle assessment (LCA).

This article is the first one to evaluate the environmental impact of passivation using nitric and citric acids. It uses attributional life cycle assessment (ALCA) to assess the environmental benefits and disbenefits of using citric acid—produced biologically via fermentation to replace nitric acid while keeping the same level of corrosion resistance. The work is anticipatory in nature as the process is not yet undertaken on a commercial basis. The results therefore feed into future manufacturing and design.

Citric and nitric acids were compared using three different solutions: a 4% citric acid solution, 10% citric acid solution, and 10% nitric acid solution (the conventional case). The results show that a scenario using a 4% citric acid solution is environmentally preferable to nitric acid across all impact categories assessed. However, a 10% citric acid solution used on low chromium and nickel steel was only environmentally preferable for 50% of the environmental impact categories assessed because of increased electrical energy demand for that scenario.

在许多行业中，腐蚀是一个严重的问题，当使用不锈钢时，要进行钝化处理以提高抗腐蚀性。传统上，在钝化步骤中使用硝酸。但是，这在生产和使用过程中会对环境和人类健康造成不利影响。减少这种影响至关重要，并且由于其毒性，相关的职业风险和特殊的处理要求，钝化不锈钢的最终用户正在探索替代的钝化方法。但是，了解任何替代方法的影响也至关重要。可持续的加工和制造体现了许多要素，包括减少浪费，资源效率措施，减少能源以及“绿色”或可再生化学品的应用。为了确保使用最有效的系统，必须对系统的影响或潜在影响进行衡量，并对选项进行比较。可以使用诸如生命周期评估（LCA）之类的工具来评估生物基化学品的相对环境资质。

本文是第一个评估使用硝酸和柠檬酸钝化对环境的影响的文章。它使用归因生命周期评估（ALCA）来评估使用柠檬酸的环境效益和弊端，柠檬酸是通过发酵生物替代硝酸而产生的，同时又保持了相同的耐腐蚀性。由于该过程尚未在商业上进行，因此该工作本质上是预期性的。因此，结果可用于将来的制造和设计。

使用三种不同的溶液对柠檬酸和硝酸进行比较：4％柠檬酸溶液，10％柠檬酸溶液和10％硝酸溶液（常规情况）。结果表明，在所有评估的影响类别中，使用4％柠檬酸溶液的方案在环境上比硝酸在环境上更可取。但是，在评估的50％环境影响类别中，在低铬和镍钢上使用10％柠檬酸溶液仅在环境方面更可取，因为这种情况下的电能需求增加。