A solidification/stabilization process for wastewater treatment sludge from a primary copper smelter

Abstract

Wastewater treatment sludge from a primary copper smelter is characterized as hazardous waste that requires treatment prior to disposal due to its significant contents of heavy metals and arsenic. The aim of the presented study was to investigate the feasibility and the effectiveness of a solidification/stabilization process of the sludge using fly ash and lime as binders. The effectiveness of the process was evaluated by Unconfined Compressive Strength (UCS) testing, leaching tests (EN 12457-4 and Toxicity Characteristic Leaching Procedure (TCLP)) and Acid Neutralization Capacity (ANC) tests. All the samples reached the target UCS value of 0.35 MPa. The calcium to silicon concentration ratio (cCa/cSi), determined by X-ray fluorescence analysis, was identified as main factor governing strength development. Inductively coupled plasma-optical emission spectrometry analyses of solutions after leaching tests showed excellent stabilization of Cu, Ni, Pb and Zn (above 99 %) and arsenic (above 90 %) in samples with high Ca(OH)2 content. Results of the ANC test indicated that the buffering capacity of solidified material linearly depended on Ca concentration in FA and lime. Samples with 20 % of binder having 50 % of FA and 50 % of lime met all the requirements for safe disposal.

Mulj koji nastaje tretmanom otpadne vode iz primarne topinice bakra predstavlja opasan otpad koji se mora tretirati pre odlaganja usled visokog sadržaja teških metala i arsena. Cilj prezentovanog rada je ispitivanje izvodljivosti i efikasnosti procesa solidifikacije/stabilizacije ovog mulja korišćenjem letećeg pepela i hidratisanog kreča kao agensa za stabilizaciju. Efikasnost procesa se određivala merenjem pritisne čvrstoće (UCS) solidifikata, testovima luženja (EN 12457-4 i Toxicity Characteristic Leaching Procedure (TCLP)) i testom kapaciteta za neutralizaciju kiseline (ANC test). Svi ispitivani uzorci su imali pritisnu čvrstoću iznad zahtevanih 0,35 MPa. Odnos koncentracija kalcijuma i silicijuma (cCa/cSi) u uzorcima, određen rendgensko-fluorescentnom analizom, je identifikovan kao glavni faktor razvoja pritisne čvrstoće. Optička emisiona spektrometrijska analiza sa indukovano spregnutom plazmom rastvora nakon testova luženja je pokazala odličnu stabilizaciju Cu, Ni, Pb i Zn (iznad 99 %) i arsena (iznad 90 %) u uzorcima sa visokim sadržajem Ca(OH)2. Rezultati ANC testa ukazuju na to da puferski kapacitet solidifikovanog materijala linearno zavisi od koncentracije Ca u letećem pepelu i kreču. Uzorak sa 20 % veziva sastava 50 % leteći pepeo i 50 % hidratisani kreč ispunjava sve zahtevane uslove da bude bezbedno odložen.