Physicochemical reaction-based allocation for the resource consumption of hydrometallurgical processing of rare-earth oxides-a case study on ion adsorption-type rare-earth oxides in China

PurposeThe growing demand for rare-earth elements has led to interest in assessing the environmental impacts of their production. However, most existing procedures only consider a small part of the life cycle of rare-earth elements. Therefore, this study proposed an allocation model for the resource consumption of multi-output products in hydrometallurgical systems based on input-output physicochemical parameters.MethodsThe basic methodological idea of this study is that resource inputs to a multi-output hydrometallurgical process should be allocated based on how they are consumed in the process. The resources consumed by the multi-output hydrometallurgical process were analyzed according to the form of consumption. Then, the basis for the allocation of the various types of resource consumption was determined by the physicochemical reaction between resource input and metal output. The allocation model was applied to the production of ion adsorption-type rare-earth oxides, and the results of the allocation were compared with the conventional mass allocation method.Results and discussionThe results indicated that, whether the allocation results were obtained based on the physicochemical reaction model or the mass model, resources consumed of Y2O3 accounted for the largest proportion, with differences of 4.81-6.01% between the two allocation results. In addition, the allocation factor for Nd2O3 production ranged from 17-18%, which was approximately 1.5% lower than the allocation factor based on the mass model. The assignment results, except for Y2O3, were higher when based on the mass model than when based on the physicochemical reaction model for all eight environmental impact types. The smallest changes were observed in La2O3 (3.75-5.74%) and Nd2O3 (7.72-9.13%). The largest change was observed for Er2O3 (15.02-20.43%).ConclusionsIn a multi-input/output system, the allocation of life cycle inventory for single rare-earth oxides or metals has an important impact on the accuracy of the environmental impact assessment results. Data deviations in the life cycle inventory of a certain production process may be magnified, impacting decision-making results. The model can help solve the problem of co-occurring metal inventory allocation based on physicochemical parameters and improve the accuracy of rare-earth product inventories.