Effect of attapulgite calcination on heavymetal adsorption from acid mine drainage

Attapulgite calcined at 973.15K was characterized and utilized as an adsorbent for the removal of heavy metals and neutralization of acid mine drainage (AMD) from a gold mine. Batch adsorption experiments were carried out using a thermostatic shaker. Activated attapulgite showed that it can neutralize AMD as it raised the pH from 2.6 to 7.3 after a residence time of 2 h. Metal ion removal after 2 h was 100% for Cu (II), 99.46% for Fe (II), 96.20% for Co (II), 86.92% for Ni (II) and 71.52% for Mn (II) using a 2.5% w/v activated attapulgite loading. The adsorption best fit the Langmuir isotherm; however, Cu (II), Co (II), and Fe (II) data fit the Freundlich isotherm as well. Calcination at 973.15 K resulted in the reduction of the equilibrium residence time from 4 to 2 h, solid loading reduction from 10 to 2.5% m/v and an increase in maximum adsorption capacity compared with unactivated attapulgite

Effect of ethylene maleic anhydride on the particulate processes during hydrogen reduction of nickel ammine sulphate solutions

Abstract: The use of additives in the precipitation of nickel with hydrogen is known to influence the particulate processes and, by extension, powder properties such as morphology, microstructure and particle size distribution. Controlling these properties is crucial for some downstream processes. The present study assesses the effect of ethylene maleic anhydride on the particulate processes taking place during the reduction of nickel ammine sulphate solutions by hydrogen gas. Reactions were carried out in an autoclave operated at 28 bar and 180°C under stirring conditions of 850 rpm. Particulate processes were studied by analysing the particle size distribution and the corresponding normalized moments. These were further validated by scanning electron microscopy and nitrogen physisorption analyses. The powder phase identification and purity were determined by means of X-ray diffraction and X-ray fluorescence, respectively. Ethylene maleic anhydride acted as a growth inhibitor and an anti-agglomerating agent, thus acting as a reduction catalyst by maintaining the available surface area for reduction. The system was dominated by agglomeration at low concentration (2–5 mg/L) of ethylene maleic anhydride while breakage became the dominant particulate process at higher concentration (7–10 mg/L), as validated by scanning electron micrographs

Effect of calcium lignosulphonate on the particulate processes during hydrogen reduction of nickel ammine sulphate solutions

Abstract: The use of additives in the precipitation of nickel with hydrogen is known to influence the particulate processes and by extension the powder properties such as morphology, microstructure and particle size distribution. Controlling these properties is crucial for some downstream processes. The present study assesses the effect of calcium lignosulphonate on the particulate processes taking place during the reduction of nickel ammine sulphate solutions by hydrogen gas. Reactions were carried out in an autoclave operated at 28 bar and 180°C under stirring conditions of 850 rpm. Particulate processes were studied by analysing the particle size distribution and the corresponding normalized moments. These were further validated by scanning electron microscopy and nitrogen physisorption analyses. The powder phase identification and purity were determined by means of X-ray diffraction and X-ray fluorescence respectively. Calcium lignosulphonate acted as a reduction catalyst, growth promoter and by extension agglomerating agent. At 2, 5 and 7 mg/L of calcium lignosulphonate, the system was found to be dominated by breakage while agglomeration was more pronounced at 10 mg/L, as validated by scanning electron micrographs. Furthermore the use of calcium lignosulphonate resulted in the increase of the reduction rate, indicating that this additive acted as a growth promoter

Synthesis and evaluation of basic oxygen furnace slag based geopolymers for removal of metals and sulphates from acidic industrial effluent-column study

Abstract:Basic Oxygen furnace slag (BOFS) based geopolymers with open porosity ranging from 21%–57 % and density between 1255 kg/m3-2432 kg/m3 were synthesized. The synthesized geopolymers potential; to be used as attenuators for metal removal and neutralization of Acid Mine Drainage (AMD); were assessed and evaluated through column test studies conducted over a period of 133 days. The results show that BOFS based geopolymer composites can be used as attenuators as over 99 % metals were removed during the first 50 days. The results also revealed that higher porosity promoted greater neutralizing ability by dissolution of soluble salts from the BOFS based geopolymer; which improves the removal efficiencies of sulphates, metals and neutralization of AMD. Characterization of the composites after contact with AMD revealed that gypsum was the main mineral phase in the geopolymers indicating that precipitation was the major mechanism that enhanced metal and sulphates removal. BOFS based geopolymers can be used to replace armoring neutralizing agents such as limestone. The research contributes to sustainable development by addressing the environmental pollution posed by AMD and utilization of BOFS as a medium for remediation of AMD. The utilization of BOFS for remediation of AMD mitigates and responds to the environmental problems and demands associated with such waste

Fixed bed column studies for decontamination of acidic mineral effluent using porous fly ash-basic oxygen furnace slag based geopolymers

Abstract: This paper presents column studies conducted to evaluate and assess the potential use of Fly Ash (FA). Basic Oxygen Furnace Slag (BOFS) based geopolymers to remove metals, sulphates and acidity from Acid Mine Drainage (AMD). Geopolymers were prepared using NaOH, Fly ash (FA) was used as source of silica additive to supplement BOFS. The blending ratio was fixed to 10% FA and the S/L ratio was kept 20%. The H2O2 was used as a blowing agent to increase the porosity of the FA/BOFS based geopolymer at four different percentages (1.5%, 1%, 0.5% and 0%). The four different geopolymers with distinct porosities were employed in different columns respectively. It was found that over 99% removal efficiency of metals and sulphates was achieved in the first 60 days of column studies. The dissolution of Ca(OH)2 was the main constituent responsible for the removal of acidity in AMD. Characterization revealed that precipitation was the main mechanism for removal of metals. Gypsum was the main byproduct formed with precipitated metals presented by goethite, spertite and manganite

Development of lightweight construction blocks by alkaline activation of BOF slag

Abstract: Large quantities of basic oxygen furnace (BOFS) are dumped in landfills of which the available land for land-filling of large quantities of waste is reducing all over the world. It is therefore im-portant to develop processes which beneficiates solid waste; BOF slag specifically. The present study attempts to investigate the potential to synthesize BOF slag based light weight construc-tion blocks. The effects of several factors on the UCS of BOF slag based light weight construc-tion blocks (LWCB) was also investigated. The test variables were molarities of sodium hydrox-ide (NaOH) (5 M, 10 M and 15 M); the solid to liquid ratio (20 %, 25 % and 30 %); the sodium silicate (Na2SiO3) to Na! OH ratio (0.5:1, 1:1, 1.5:1, 2:1, 2.5:1 and 3:1); the curing temperature (40°C, 80°C and 100°C). It was found that optimum synthesis conditions were 5M NaOH, 80°C and 1:1 Sodium Silicate: NaOH ratio. The LWCB composite met the minimum requirements for ASTM C34-13, C129-14a and South African standard (SANS227: 2007)

Removal of sulphates from acid mine drainage using desilicated fly ash slag

Abstract: The removal of sulphates from acid mine drainage (AMD) using desilicated fly ash (DFA) was investigated. The effects of DFA solid loading, residence time and removal temperature were investigated. A 2% DFA solid loading gave the highest sulphate removal of 75% at a temperature and residence time of 35ºC and 90 min respectively. The maximum adsorption capacity for DFA was found to be 147.06 mg/g DFA. The sorption mechanism followed the Langmuir isotherm and pseudo second order kinetics. The Gibbs free energy and enthalpy for the sorption was found to be 17.26 and 125.096 J/mol respectively. This research showed that DFA was an attractive alternative adsorbent for sulphates in AMD

Reduction crystallization of Ni, Cu, Fe and Co from a mixed metal effluent

Abstract: Removal and recovery of heavy metals from effluent are major concerns due to diminishing fresh water resources, depletion of exploitable ores and human and environmental health concerns. The objective of this work was to efficiently recover heavy metals from effluent in their elemental form as metallic powder by reduction crystallization. This method recovers metals in a pure form and enables them to be directly used. Experiments were conducted using mixed metal solutions of Ni, Cu, Co, and Fe in a 20 L Perspex batch reactor using hydrazine as a reducing agent and nickel powder as seeding material. Ni, Cu, Co and Fe were effectively reduced to their elemental states with removal efficiencies of over 99% for Ni and Co and about 98% for Cu and Fe. Residual concentrations obtained for Ni, Co and Fe were below 0.05 mg/L and below 1.20 mg/L for Cu. Based on the evolution of the particle size distribution (PSD) and its derived moments the dominant particulate processes identified were aggregation, growth and breakage with the possibility of nucleation in the presence of Fe. However, particle size enlargement was largely due to aggregation

The removal of Ni & Cu from a mixed metal system using sodium borohydride as a reducing agent

Abstract: Removal of nickel (II) and copper (II) from aqueous solutions using NaBH4 as a reducing agent was studied. Reduction crystallization was achieved in a batch reactor at 65oC using seeded experiments. The effect of using different molar ratios of [Ni2+]:[BH4-] namely; 1:1, 1:0.25 and 1:0.1 and seeding materials on the rate of reduction was also investigated. The results obtained showed that NaBH4 is an effective reducing agent for the removal of Ni2+ and Cu2+ from effluents. Using a molar ratio of 1:0.1 of [Ni2+]:[BH4-] and Fe and Ni as a seeding material over 99% metal removal was achieved. Ni as a seeding material yielded the best results as it is autocatalytic although there was no significant difference in the rate of reduction compared to that obtained when Fe was used as a seeding material

Silicon and aluminium leaching kinetics from acidic gold mine tailings

Abstract: . Si and Al were leached from gold mine tailings (GMT) in order to determine if the GMT could be used as precursors for the synthesis of geopolymers. Possible synthesis of geopolymers from GMT would help reduce their potential pollution effects through heavy metal immobilisations. The effect of type of alkali (NaOH/KOH), alkali concentration, temperature, milling and calcination of GMT and solid liquid ratio (S/L) on the leaching of Si and Al was investigated. The optimum conditions were 10 M KOH, S/L of 0.5% m/v and a leaching temperature of 95ºC. The leaching obeyed the shrinking core model with the surface chemical reaction being the controlling step. The leaching of Si was linked to the Al leaching since the Si/Al ratio of the leachate was around 2 irrespective of leaching conditions. KOH yielded more Si and Al. as compared to NaOH, with 54.7 and 26.7 Si and Al leached respectively from as received GMT. Calcination at 900ºC resulted in 18% and 22 % increase in Si and Al yield respectively for KOH based leaching. The successful leaching of Si and Al from GMT using KOH provides opportunities for the geopolymerisation of GMT thereby allowing the minimisation of their pollution effects