Recovery of the Phosphorus from the Nitric Acid Extract of Powder Collected in a Bag Filter during the Recycling of Used Fluorescence Tubes

Abstract

During the recovery of phosphorus from the powder collected in a bag filter during the recycling of used fluorescence tubes (bag-powder), the batch method with aqueous HNO₃ was used to examine the elution behavior of aqueous phosphate contained in the bag-powder. The main components of the bag-powder included Ca²⁺, PO₄³⁻ and Y³⁺ along with Si⁴⁺, Sr²⁺ and lanthanide cations such as La³⁺ and Ce⁴⁺. Therefore, it seemed possible that, with the selective dissolution of Ca²⁺ and PO₄³⁻ from the bag-powder, these lanthanide cations in the residue could be enriched. With the batch method, most of the phosphate in the bag-powder was dissolved within 0.2 min using 1.0 mol/L HNO₃. The dissolution behavior of calcium cation was similar to that of the phosphate. In contrast, the dissolution of yttrium, the content of which was the highest among the lanthanide cations in the bag-powder, was increased with the dissolution times, reaching complete dissolution after 24 h. The Sr²⁺, La³⁺ and Si⁴⁺ in the bag-powder, however, did not dissolve under the same conditions. Although Ca²⁺, PO₄³⁻ and Y³⁺ were the main components in the nitric acid extract, Y³⁺ was separated as YPO₄ at pH=4.0, while Ca²⁺ and PO₄³⁻ were separated as calcium phosphates at pH=7.0. These results revealed that the separation of calcium phosphates, YPO₄ and some residue was possible, and resulted in the enrichment of lanthanide cations along with the recovery of phosphorus from the bag-powder. Using the present technique, 91% of the P in the bag-powder was recovered.