K-Struvite Precipitation from Source-separated Battery Wastewater

Abstract

Abstract

Recovering nutrients from spent alkaline battery wastewater is important for environmental sustainability and resource management. Battery manufacturing and recycling processes often generate wastewater that contains a substantial amount of K+. The current study aimed to evaluate the recovery efficiencies of K+, PO43-, and Mg2+. This was achieved by precipitating Magnesium potassium phosphate hexahydrate (MPP) using three different models. In Model 1, the pH levels were adjusted to the desired levels (7, 10, 10.5, 11, 11.5, and 12) using NaOH. The highest recovery efficiencies for K+ and PO43- were 34.7 % and 52 % at a 1:1:1 molar ratio of Mg:K:P, while Mg2+ recovery ranged from 97 % to 100 %. In Model 2, the pH was maintained at pH 7. The K+ removal efficiency ranged from 47.5 % to 54.8 %. In Model 3, the experiment compared two different MgO’s at pH 7. By comparison, the results show that the maximum recovery of K+ reached 65.1 % for MgO (95 %) and 59.5 % for MgO (71 %), respectively. The precipitates obtained were characterized through XRD, SEM-EDS, and ICP analysis. XRD confirmed a dominant pattern of K-struvite at a specific molar ratio of Mg:K:P of 0.5:1:0.5. Additionally, ICP analysis indicated that the permissible purity limits for heavy metals in fertilizers in Finland could be achieved at a pH of 7 for K-struvite. This study underlines the importance of considering optimal pH and Mg:P molar ratios for removing K+ from spent alkaline battery wastewater to produce purified K-struvite and prevent impurity compounds.