Sulfuric Acid Baking—Water Leaching for Gold Enrichment and Arsenic Removal from Gold Concentrate

During the roasting of gold concentrate to improve gold recovery, arsenic is released into the air and valuable elements such as Fe, Cu, Zn, and Pb are converted into oxide minerals. In this research, we evaluated the release of As and the loss of valuable metals during the acid baking and hot water leaching processes used for gold concentrate. The acid bake tests were conducted for gold concentrate using an electric furnace by applying various concentrations of H2SO4 solution under different baking times. The water leaching process was enacted using 70 °C water for the baked samples. Chemical and mineral compositions of the raw and treated samples were analyzed using AAS and XRD, respectively. The results show that soluble metal sulfates, such as rhomboclase and mikasite, were formed in the baked samples, and that the leaching of valuable metals (Fe, Cu, Zn, and Pb) was accelerated during the hot water leaching procedure. During acid baking, arsenic was partially removed by volatilization, and the rest of the arsenic-containing minerals were converted to soluble minerals. The soluble arsenic-containing mineral resulted in a dissolution that was 60 times higher than in the roasted sample. The maximum gold grade of solid residues increased up to 33% through the acid baking–water leaching process. It was confirmed that acid baking with H2SO4 prevented As release into the air, as well as the recovery of valuable metals through hot water leaching, such as Fe, Cu, Zn, and Pb, which were formerly discarded in the tailings.

Ecological Risk Indicators for Leached Heavy Metals from Coal Ash Generated at a Malaysian Power Plant

The application of coal ash (CA) in construction industries has grown rapidly, posing risk to the environment due to heavy metals leaching from the material. This research presents a simulation of ecological risk assessment and model risk indicators (ERI) of leached heavy metals (lead (Pb), copper (Cu), zinc (Zn) and arsenic (As)) from CA (FA: fly ash and BA: bottom ash) via response surface methodology (RSM). The ERI values were based on quantified leached heavy metals from the toxicity characteristic leaching procedure (TCLP-1311) and synthetic precipitation leaching procedure (SPLP-1312). The ecological risk index (RI ) values for TCLP were 10.27 × 100 (FA), 9.91 × 100 (BA) and 12.58 × 100 (FA + BA); whereas RI for SPLP were 10.34 × 100 (FA), 9.90 × 100 (BA) and 12.61 × 100 (FA + BA). Twenty-nine combinations of operations were evaluated based on Box-Behnken design with ERI as the response variable. The established model risk indicator (i.e., coded and actual factors) of Pb, Cu, Zn and ‘As’ showed significant model terms that describe their relationship very well, perfectly fit to the corresponding ERI (sum of squares = 0.4160, F value = 682,375.55) with probability of 0.01% for an F-value could occur due to noise. The optimized models were validated with error percentage of less than 5%. The established ERI models showed significant model terms and will be useful for ecological monitoring of CA application in construction industries.

Speciation and environmental risk of heavy metals in biochars produced by pyrolysis of chicken manure and water-washed swine manure

This study was conducted to investigate the speciation, bioavailability and environmental risk of heavy metals (HMs) in chicken manure (CM) and water-washed swine manure (WSM) and their biochars produced at different pyrolysis temperatures (200 to 800 °C). As the pyrolysis temperature increased, the remaining proportion, toxicity characteristic leaching procedure (TCLP), HCl and diethylenetriamine pentaacetic acid (DTPA) of HMs gradually declined. This result proved that the speciation of HMs in chicken manure biochars (CMB) and water-washed swine manure biochars (WSMB) was influenced by pyrolysis temperature. The proportions of stable fractions were enhanced with increased pyrolysis temperature and weakened the HM validity for vegetation at 800 °C. Finally, the results of the risk assessment showed that the environmental risk of HMs in CMB and WSMB decreased with increasing pyrolysis temperature. Therefore, pyrolysis at 800 °C can provide a practical approach to lessen the initial and underlying heavy metal toxicity of CMB and WSMB to the environment.

A Comparison in Metal Leachability Between Phosphoric Acid and Ascorbic Acid Stabilised Ferrochrome Slag

Ferrochrome (FeCr) slag was milled and stabilised with either ascorbic acid or phosphoric acid. The stabilised FeCr was then geopolymerised with 1 M KOH in order to obtain a monolith with at least an unconfined compressive strength of 1 MPa. The leachability of metals of the stabilised geopolymerised monoliths were then compared with the unstabilised geopolymerised monolith. Ascorbic acid stabilisation was only effective in Cr leaching reduction by 99.45% but was not effective on immobilisation of Fe, Zn, Ni and Mn. Ascorbic acid stabilisation was thought to proceed via the reduction of Cr(VI) species to insoluble Cr (III) species. Phosphate stabilisation reduced the leachability of Cr, Ni, Zn, Mn, Fe by 99.5%, 67.1%, 71.1%, 96.8% and 85.4% respectively. Phosphate stabilisation was thought to proceed via the formation of phosphate compounds of the metal ions in question. The phosphate stabilised FeCr slag leachability was within the allowable Toxicity Characteristic Leaching Procedure (TCLP) limits and its use is not detrimental to the environment.

POTENSI LIMBAH B3 SPENT BLACHING EARTH SEBAGAI BAHAN BAKAR PADA INDUSTRI MINYAK GORENG PT. ABC

SBE (spent bleaching earth) sebagai hasil samping dari pemakaian bleaching earth pada proses fraksinasi produksi minyak dan proses produksi SCD (semi continous deodorizer) sebagai residu sisa filtrasi. Kondisi eksisting pada industri X, sekitar 8.196,890ton/tahun LB3 SBE belum dimanfaatkan dan belum diolah yang dilakukan secara mandiri. Penelitian ini bertujuan untuk mendapatkan potensi dari LB3 SBE sebagai campuran bahan bakar pada PT. ABC. Metode yang digunakan adalah dengan uji kualitas batu bara (bahan bakar eksisting) dan uji kulitas pada LB3 SBE dengan parameter logam berat, kadar air dan nilai kalor. Dari hasil penelitian didapatkan kualitas batu bara yang digunakan cukup bagus karena memiliki kandungan sulfur, volatile dan fix carbon yang rendah. Emisi cerobong masih memenuhi baku mutu sesuai Permen LH No. 07 Tahun 2007. Sedangkan pada TCLP (Toxicity Characteristic Leaching Procedure), didapatkan SBE masuk kategori 1 (bersifat berbahaya) sebagai LB3 karena nilai TCLP yang lebih banyak pada kategori A. Dari uji nilai kalor dan kadar air, SBE sangat berpotensi untuk dimanfaatkan sebagai bahan bakar karena memenuhi syarat minimal sebagai bahan bakar (11 MJ/kg atau setara dengan 2.627,305 Kkal/kg dan 2,5%). Potensi LB3 SBE untuk dimanfaatkan sebagai bahan bakar sangat tinggi, baik dari segi kuantitas maupun kualitas dihasilkan pada industri pengolahan kelapa sawit.

Imobilização de metais pesados presentes nos resíduos de quartzito por meio da incorporação em argamassas com substituição total do agregado natural

RESUMO Este trabalho objetivou imobilizar metais pesados presentes nos resíduos de quartzito por meio da incorporação em argamassas em substituição total ao agregado natural. Dois tipos de resíduos foram utilizados: os resíduos de fragmentação das aparas (QS) e os do pó de serragem (QP). Os resíduos foram caracterizados por fluorescência de raios X, difração de raios X e ensaios de toxidade conforme metodologia da Norma Brasileira (NBR) 10005, da NBR 10006 e do Toxicity Characteristic Leaching Procedure (TCLP) 1311. Então, foram analisadas composições de argamassas contendo cimento, cal e os resíduos (QS, QP) utilizando-se a técnica de delineamento de mistura, determinando os melhores traços, o melhor tipo de cura (imersa ou úmida) e, posteriormente, avaliando a resistência dos corpos de prova após cura. A caracterização do resíduo de quartzito revelou a presença de vários metais pesados e extratos lixiviados em contato com a água, classificando-o como resíduo de Classe I — Perigoso. Os resultados indicam que as composições determinadas foram capazes de imobilizar os metais pesados presentes nos resíduos de quartzitos, bem como resultou em argamassas com resistências mecânicas superiores a 2 MPa. Por fim, mostrou-se que essa técnica de solubilização e estabilização dos contaminantes presentes nos resíduos de quartzito é uma alternativa tecnologicamente viável e ambientalmente adequada para a destinação final desses resíduos.