Simultaneous harmless treatment of barium slag and manganese residue via a multiple water alternating washing process

Barium slag (BS) is a hazardous waste generated during the industrial production process of barium salts, posing serious threats to ecological environment due to its high soluble Ba concentration and high pH. The development of efficient harmless treatment technologies is imperative for BS management. In this study, the Ba dissolution behavior of BS implied that washing with 20 rounds of water could reduce the soluble Ba but cannot achieve harmless treatment. Based on manganese residue (MR) containing soluble MnSO₄, an innovative process involving the alternating washing of MR and BS with water, was proposed to simultaneously achieve harmless treatment of BS and reduction of soluble Mn in MR. The conditions used in the process were optimized as follows: MR/BS mass ratio of 50 g/100 g, washing temperature of 25 ℃, washing time of 60 min, and alternating washing for 5 rounds. Under these conditions, treated BS had a Ba extraction toxicity concentration of 25.60 mg/L, decreasing from 1725 mg/L for the original BS, with the pH decreasing from 12.52 to 11.64, and the treated MR had a soluble Mn of 34.20 mg/L from 1900 mg/L of the original MR. Water transferred‌ soluble ions from one waste to form BaSO₄ or Mn(OH)₂ precipitates, as confirmed by XRD, SEM, and XPS. Additionally, the final washing solution was recyclable for another two water alternating washing processes, with potassium accumulation from 61.1 to 181 mg/L. These findings provide a simple, green, and low-cost technical route for treating BS and MR in production practice.