Alkaline lead in an innovative recycling process with pretreatment, stabilization and solidification

Olovna alkalna šljaka je otpad koji se generiše u pirometalurškom procesu prerade olovnih sirovina, sa dodatkom topitelja natrijum(I)-karbonata (Na2CO3). U izradi doktorske disertacije ispitivan je kombinovani proces prerade olovnih sirovina iz primarnih i sekundarnih izvora, kao i mogućnost predtretmana, stabilizacije i solidifikacije industrijskog uzorka olovne alkalne šljake iz procesa reciklaže istrošenih olovnih akumulatora. U prvom delu istraživanja analiziran je proces topljenja olovnih sirovina u kratkoj rotacionoj peći, u laboratorijskim uslovima. U procesu su korišćeni olovni koncentrat (primarna sirovina) i desumporizovana olovna pasta (sekundarna sirovina), posle njihove detaljne karakterizacije, ispitivanja hemijskog i granulometrijskog sastava olovnog koncentrata, kao i hemijskog sastava desumporizovane olovne paste. Topljenje je ispitano u funkciji sastava šarže, temperature, rotacije i vremena zadržavanja materijala u peći. Efikasnost procesa topljenja je procenjena na osnovu ostvarenog stepena ekstrakcije olova iz sirovina, fizičko-hemijskih osobina (hemijski sastav, bazicitet, viskozitet) i količine generisane šljake. Najbolji rezultat efikasnosti ekstrakcije olova (98,38 %) je ostvaren u eksperimentu sa kombinovanim topljenjem olovnog koncentrata (50 %) i desumporizovane olovne paste (50 %). Generisana je šljaka u količini od 32 % u odnosu na masu polaznih sirovina, sa sadržajem 3,34 % olova, u kojoj su metodom rentgenske difrakcije (XRD - X-ray diffraction) identifikovane faze Na4Ca4(Si6O18), Fe2SiO4 i FeO(OH), manje količine faze CaFe2O4, i najmanje faze FeO. Zbog korišćenja relativno čistih sirovina u pogledu primesa, količina As u generisanoj šljaci je bila niska (0,003 %). Viskozitet generisane šljake od 60 P (kg/(m·s)), na temperaturi 1100 °C, bio je zadovoljavajući u pogledu dobrog razdvajanja šljake od metala, a izračunata vrednost baziciteta od 0,85 je ukazala na njen blago kiseli karakter. Drugi deo istraživanja obuhvatio je ispitivanje procesa predtretamana industrijskog uzorka olovne alkalne šljake, generisane u procesu reciklaže istrošenih olovnih akumulatora. Ispitano je luženje elemenata (Na, S, As, Fe, Pb) iz šljake u vodi, u reakcionom balonu (diskontinualno ispiranje) i u inovativnom uređaju, cilindričnom-rotirajućem ispirač-odvajaču (kontinualno ispiranje). Istraživanje je obuhvatilo ispitivanje mogućnosti uklanjanja u vodi rastvornih komponenata šljake, maksimalnu valorizaciju korisnih komponenata i minimizaciju otpadnih tokova iz procesa. Polazna šljaka je detaljno karakterisana, određen je hemijski i granulometriski sasatav, promena mase i granulacije šljake sa vremenom, rastvorljivost u vodi i proces luženja elemenata po standardnim procedurama (Toxicity characteristic leaching procedure – TCLP, EN 12457-2). Rezultati su ukazali na opasnu i specifičnu prirodu olovne alkalne šljake, što se ogleda u higroskopnosti, formiranju praškaste forme sa skladištenjem u atmosferi vazduha, rastvorljivosti u vodi i sadržaju toksičnih i migratornih elemenata koji mogu ugroziti životnu sredinu. Proces luženja Na, S i As iz šljake u vodi je bio dominantan. Uticaji odnosa tečno:čvrsto (L/S), brzine mešanja rastvora (w) i temperature (T) na luženje elemenata iz šljake ispitani su u funkciji vremena. Maksimalne vrednosti stepena izluženja Na od 95,78 %, S od 75,34 % i As od 79,89 % su proračunata za L / S = 20, w = 600 min-1, T = 333 K i 120 min izvođenja eksperimenta. Analiza kinetičkih parametara procesa luženja As je ukazala na model tro-dimenzione difuzije, sa energijom aktivacije 15,55 kJ∙mol-1. Luženje Na i S je objašnjeno po modelu dvo-stepene difuzije kroz cilindričan sloj proizvoda, sa energijama aktivacije 18,71 kJ∙mol-1 i 17,24 kJ∙mol-1, redom. Rezultati dobijeni u diskontinualnom procesu ispiranja šljake sa vodom su korišćeni u optimizaciji patentiranog procesa kontinualnog predtretmana olovne alkalne šljake u inovativnom uređaju, cilindričnom-rotirajućem ispirač-odvajaču (T = 313 K, L/S = 10, w = 200 min-1 sa podešavanjem vremena zadržavanja). U procesu kontinualnog ispiranja od 60 min proračunati su maksimalni stepeni izluženja Na 45 %, S 45 % i As 70 %, kao i stepen iskorišćenja Na2SO4 iz rastvora od ispiranja do 10 %, u odnosu na fazu desumporizacije paste. Sa ispiranjem šljake u diskontinulanom procesu (L / S = 20, w = 600 min-1, T = 333 K i 120 min), ostvareno je smanjenje mase od oko 30 %, a u kontinualnom procesu (L/S = 10, w = 200 min-1, T = 313 K, sa podešavanjem vremena zadržavanja), oko 20 %. Krupnija frakcija šljake (+1 mm), bogata metal-sulfidnim komponetama (kamenac), vraćena je u proces topljenja, u cilju valorizacije korisnih metala. Sitnija frakcija šljake (-1 mm), karakterisana je u opasnu vrstu otpada po TCLP testu, zbog koncentracije Pb u kiselim (pH ~3) lužnim rastvorima iznad maksimalno dozvoljene koncentracije (MDK) (5,00 mg·L-1), i dalje korišćena u pocesu stabilizacije i solidifikacije (S/S)...Alkaline lead slag is a waste generated in the pyrometallurgical process of the recycling of materials based on lead with the addition of a sodium(I)-carbonate (Na2CO3) as a flux. The doctoral dissertation includes investigation of a combined process of recycling of lead materials from primary and secondary sources, as well as the possibility of pre-treatment, stabilization and solidification of the industrial sample of lead alkaline slag from the recycling process of spent lead acid batteries. In the first part of the research, the smelting process of lead materials in a short rotary furnace was examined in laboratory conditions. In the process, lead concentrate (primary raw material) and desumporized lead paste (secondary raw material) were used, after their detailed characterization including chemical and granulometric composition of the lead concentrate, as well as the chemical composition of the desumporized lead paste. The smelting process was tested in the function of the batch composition, temperature, rotation and process time in the furnace. The efficacy of the smelting process was estimated based on the achieved degree of extraction of lead from raw materials, physical and chemical properties (chemical composition, basicity, viscosity) and quantities of generated slag. The best result of the extraction efficiency of lead (98.38 %) was obtained in an experiment with combined smelting of lead concentrate (50 %) and desumporized lead paste (50 %). Slag is generated in the amount of 32 % in relation to the weight of the charge, with a content of 3.34% of lead. XRD analysis of the slag showed Na4Ca4 (Si6O18), Fe2SiO4 and FeO as the main phases (OH), less CaFe2O4, whereas FeO was the least present. Due to the use of relatively pure raw material in charge mixture, the amount of As in the generated slag was low (0.003 %). The viscosity of the generated slag was 60 P (kg/(m·s)) at 1100 ° C, which was satisfactory in terms of the good separation of the slag from the metal, and the calculated value of the basicity of 0.85 indicated its slightly acidic character. The second part of the study included the investigation of the pre-treatment process of the industrial sample of alkaline lead slag generated in the recycling process of spent lead-acid batteries. The water leaching of elements (Na, S, As, Fe, Pb) from the slag, in a reactior (discontinuous leaching) and in the innovative device, with a cylindrical-rotating washer-separator (continuous leaching) was examined. The research included the study of the possibility of removing of water soluble components from the slag, the maximum valorization of useful components, and the minimization of waste streams from the process. The starting slag is characterized. Its chemical composition, granulometric composition, mass change and slag granulation with time, solubility in water and treatment according to standard procedures (TCLP, EN 12457-2) are determined. The results of the characterization of alkaline lead slug pointed to its hazardous and specific nature (hygroscopicity, time delamination, solubility in water) and the content of toxic elements that potentially could affect the environment. Leaching degrees of Na, S and As from slag were dominant. The effects of L/S ratio, stirring speed and temperature were analyzed in the function of time. Maximum leaching degrees 95.78 % Na, 75.34 % S and 79.89 % As were determined for L/S = 20, w = 600 min-1, T = 333 K and 120 min. As kinetics was explained by the process of three-dimensional diffusion and activation energy of 15.55 kJ·mol-1. The kinetics of Na and S are explained by the two-degree diffusion model through a cylindrical layer of products, with activation energies of 18.71 kJ·mol-1 and 17.24 kJ·mol-1 respectively. The obtained results of the leaching test were used in the optimization of the patent process of the continuous pre-treatment of alkaline lead slag in the rotating-cylinder washer/separator (T = 313 K, L/S = 10, w = 200 min-1 with the setting of the retention time). In the continuous leaching process of 60 min, the maximum degree of leaching was determined Na 45 %, S 45 % and As 70 % as well as the degree of Na2SO4 utilization from the solution of 10 %, relative to the desulphurization phase of the paste. With pre-treatment of the slag in the discontinuous process, for the conditions of treatment: L/S=20, w =600 min-1, T = 333 K and 120 min, a reduction in mass of about 30% was achieved, and in the continuous process, for the elimination conditions L/S=10, w=200 min-1, T = 313 K, with adjusting retention time, about 20%. The metal-sulfide phase of the slag (fraction + 1mm) was returned to the smelting process in order to obtain useful metals. The phase of finer granulation (- 1mm) was characterized (TCLP test) as a hazardous type of waste, due to the Pb released (pH ~ 3) higher than MDK (5.00 mg·L-1) in strongly acidic conditions and further treated by stabilization/solidification process (S/S)..