Leaching kinetics of copper and valuable metal extraction from copper-cadmium residues of zinc hydrometallurgy by oxidation acid leaching

Multiple purification of zinc sulfate solution is an important process for zinc hydrometallurgy, and large quantities of copper-cadmium residues are generated as byproducts in this process. Copper-cadmium residues contain a large number of valuable metals that must be recovered. A comprehensive extraction process has been proposed using sulfuric acid as the leaching reagent and hydrogen peroxide as the oxidizing reagent. The effects of acid concentration, leaching temperature, leaching time, liquid-to-solid ratio, hydrogen peroxide dosage and stirring speed on the leaching efficiency were investigated. The optimum conditions were determined as an acid concentration of 150 g/L, liquid-to-solid ratio of 4:1, hydrogen peroxide amount of 20 mL, time of 60 min, temperature of 30 °C, particle size of −d75 μm, and agitation rate of 300 r/min. It was concluded that the leaching efficiency of copper and cadmium reached 97%, but because of the existence of zinc sulfide in the residues, a lower leaching efficiency of zinc was obtained. Furthermore, the leaching kinetics of copper was also studied based on the shrinking core model. The activation energy for copper leaching was 5.06 kJ/mol, and the leaching process was controlled by the diffusion through the product layer.

Degradation of Poly(Butylene Succinate) and Poly(Butylene Succinate)/Poly(Lactide) Blends using Serine Protease Produced from Laceyella sacchari LP175

The thermophilic filamentous bacterium Laceyella sacchari LP175 was cultivated in a 10.0 L airlift fermenter to produce serine protease at 50 °C. Maximal serine protease activity at 1,123.32 ± 15.8 U/mL was obtained for cultivation at 0.6 vvm aeration rate for 36 h. The crude enzyme was applied for degradation of poly (butylene succinate) (PBS), and poly (butylene succinate)/poly(lactide) blend (PBS/PLA) powders at 50 °C for 48 h with different substrates and enzyme concentrations. Results showed that serine protease produced from L. sacchari LP175 degraded PBS and PBS/PLA at 46.5 ± 2.05 and 49.8 ± 1.45 %, respectively, at an initial substrate concentration of 100 g/L with 1,200 U/mL of serine protease activity. Percentage degradation of PBS and PBS/PLA was improved to 51.4 ± 1.06 and 56.9 ± 1.42 %, respectively, when upscaled in a 2.0 L stirrer fermenter with 200 rpm agitation rate. Degradation products evaluated by a scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed that serine protease produced from L. sacchari LP175 degraded both PBS and PBS/PLA polymers. Results showed that microbial enzyme technology could be used to degrade PBS and PBS/PLA blend polymers and reduce the accumulation of waste. HIGHLIGHTS Upscaled serine protease production was achieved in a 10 L airlift fermenter by sacchari LP175 using low-cost agricultural products as substrate The crude enzyme degraded PBS and PBS/PLA powders (100 g/L) at up to 51.4 and 56.9 %, respectively in a 2.0 L stirrer fermenter under optimal conditions Degradation products of PBS and PBS/PLA by crude enzyme produced from sacchari LP175 were characterized GRAPHICAL ABSTRACT

Locust bean gum adsorption onto softwood kraft pulp fibres: isotherms, kinetics and paper strength

The adsorption of locust bean gum (LBG) onto Northern Bleached Softwood Kraft (NBSK) pulp improved paper tensile and burst strength and lowered refining energy by strengthening inter-fibre bonding. Adsorption kinetics and isotherms were investigated to develop a fundamental understanding of the adsorption mechanism. The adsorption rate followed pseudo-second-order kinetics and the activation energy was 99.34 kJ·mol−1, suggesting chemisorption. The adsorption rate constant increased rapidly with temperature from 25 to 45 °C (k = 1.93 to 24.03 g·mg−1·min−1), but the amount adsorbed at equilibrium decreased (qe = 1.91 to 0.48 mg·g−1 o.d. fibre). LBG adsorption to NBSK at 25 °C was consistent with the Langmuir adsorption model for LBG < 2.1 wt% of o.d. fibre, suggesting reversible, homogenous adsorption to a finite number of sites on the fibre surface. Refining to 3000 rev increased the heterogeneity of the NBSK pulp surface leading to multi-layer Freundlich adsorption with adsorption constant n = 5.00, and the equilibrium constant Kf = 2.57 mg·g−1·(mg·L−1)−1/n at 25 °C. Favorable adsorption conditions for negatively charged LBG were identified: 25 °C for 10 min, low dosage level (< 2 wt%), lightly refined (< 3000 rev) NBSK pulp at low fibre consistency (< 0.5 wt%), high agitation rate (> 150 r.p.m.), acidic or neutral conditions (pH 2–7) without salt addition. Graphic abstract

OPTIMIZATION OF PROCESS PARAMETERS FOR CULTIVATION OF BACTERIOPHAGES PROMISING FOR BIOLOGICAL CONTROL OF PHYTOPATHOGENIC BACTERIA OF GENUS PSEUDOMONAS

Cultural parameters of bacteriophages screened for lytic activity toward host bacterial strain P. helmanticensis BIM В-582 D were investigated. The following conditions were shown to be optimal for cultivation of indicator culture and it’s lysis by Pseudomonas phages BIM ВV-45 D, BIM ВV-46 D, BIM ВV-47 D, BIM ВV-50 D, BIM ВV-53 D, BIM ВV-61 D in laboratory fermenters ANKUM-3M: nutrient medium – fish meal hydrolysate broth, temperature – 28°C, stirrer agitation rate – 160 rpm, aeration rate – 1 l air/ l medium per min. Biopreparation produced under optimized conditions and composed of six afore-mentioned phages display high lytic activity both in regard to the host strain and to phytopathogenic bacteria Pseudomonas syringae.

Feasibility of the Hybrid Use of Chlorella vulgaris Culture with the Conventional Biological Treatment in Urban Wastewater Treatment Plants

Currently, most wastewater treatment plants do not meet the legal requirements, especially regarding phosphorus and nitrogen contents. In this work, real primary urban wastewater (P-UW) was used as culture medium for the growth of Chlorella vulgaris. Experiments were carried out in batch photobioreactors at laboratory scale. To determine the maximum nutrient removal levels and the optimal pH value for C. vulgaris growth, the following pH values were studied: 5, 6, 7, 8, 9, 10, and 11. Additionally, two control experiments were conducted using UW and tap water at the same conditions but without microalgae inoculation. The operational conditions were agitation rate = 200 rpm, T = 25 °C, aeration rate = 0.5 L/min, and continuous light with illumination intensity = 359 µE m−2 s−1. Significant higher growth was obtained at pH = 7. The direct use of C. vulgaris for P-UW treatment demonstrated high removal percentages of organic (COD and BOD5 removal = 63.4% and 92.3%, respectively) and inorganic compounds (inorganic carbon removal = 99.6%). The final biomass was characterized by an accumulation of high energetic compounds, mainly carbohydrates, which ranged between 63.3% (pH = 5) and 82.8% (pH = 11) and represent a source of biofuels. These new achievements open up the possibility of new horizons in urban wastewater treatment.

Dissolved oxygen as a propulsive parameter for polyhydroxyalkanoate production using Bacillus endophyticus cultures

Conventional biopolymers resembling synthetic polymers produced from microorganisms, polyhydroxyalkanoate (PHA) synthesized utilizing renewable resources have gained supreme attention recently. PHA accumulation within the microbial cell is an innate capability of bacteria to store carbon and energy when nutrient imbalance pertains. Gram positive Bacillus endophyticus capable of synthesizing PHA was focused in this study. Study focuses on the possibility of attaining high PHA yield in relation to the varying dissolved oxygen levels induced during production phase. There was a gradual increment in PHA production from 34.5 to 53.03% when cultivated in bioreactor that maintained least dissolved oxygen of 0.4 mg/L at 32 °C. The metabolic flux of organism was altered during oxygen stress brought by varying agitation rate and volume resulting in the accumulation of Nicotinamide Adenine Dinucleotide Hydrogen (NADH), which led to increase in the overall PHA production. PHA yield was found to be favored by decreasing the oxygen supply thereby inducing an oxygen stress environment. This report was the first one that was correlating the hypothesis that links PHA yield and oxygen stress condition during production phase. PHA produced was characterized by FTIR and 1HNMR spectra in which the presence of Polyhydroxybutyrate was confirmed. Graphical abstract

Optimizing the Sodium Hydroxide Conversion Using Regression Analysis in CSTR

The current study deals with the maximization of NaOH conversion using step-wise regression analysis in a CSTR. The dependence of temperature, volume, agitation rate, and feed rate on reactor performance is examined as well as interaction outcome of the operating parameters. The concentration of the reactants was fixed at 0.1 M. The steady state conversion with respect to NaOH is analyzed to find the process performance. Step-wise regression analysis is used to remove an insignificant factors. The agitation rate (X2) and feed rate (X3) proved to have an insignificant influence on the reaction conversion at a significant level (α) of 5%. Consequently, the temperature (X1) and reaction volume (X4) were found to have significant effect on the reaction conversion using step-wise regression. The temperature and volume dependence on steady state NaOH conversion were described by a polynomial model of 2nd and 3rd order. A maximal steady state conversion equal to 63.15% was obtained. No improvement was found in reaction conversion with 3rd order polynomial, so the second order polynomial is considered as the optimum reaction conversion modal. It may be recommended that 2nd order regression polynomial model adequately represents the experimental data very well.

Preparation of Polyurea Microcapsules by Interfacial Polymerization of Isocyanate and Chitosan Oligosaccharide

(2-((1-(4-chlorophenyl)-1H-pyrazol-3-yl)oxy)-N-(3,4-dichlorophenyl)-propanamide) is a new oil-soluble compound with good fungicidal activity against Rhizoctonia solani. Chitosan oligosaccharide (COS) is the depolymerization product of chitosan and can be developed into biological pesticides, growth regulators, and fertilizers due to its various bioactivities. COS is an oligomer of β- (1 → 4)-linked d –glucosamine and can be taken as a polyamine. In this study, microcapsules were prepared by interfacial polymerization of oil-soluble methylene diphenyl diisocyanate and water-soluble COS. The effects of several key preparation parameters, e.g., emulsifier dosage, agitation rate during emulsification, and core/shell ratio, on properties of the microcapsules such as the encapsulation efficiency, particle size, and size distribution were investigated. The microcapsules were characterized by infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy, etc., and the encapsulation efficiency and release behaviors were investigated. The results show that the microcapsules have a smooth surface and 93.3% of encapsulation efficiency. The microcapsules showed slow-release behavior following a first-order kinetic equation, and the accumulative release rates of the microcapsules with core/shell mass ratios of 8.0/4.0, 8.0/5.0, and 8.0/6.0, were 95.5%, 91.4%, and 90.1%, respectively, on day 30. Due to many high biological activities, biodegradability, and the pure nature of COS, microcapsules formed from COS are promising for applications in controlled release of pesticides, growth regulators, and fertilizer.

Aqueous Extraction of Seed Oil from Mamey Sapote (Pouteria sapota) after Viscozyme L Treatment

In this study, aqueous enzymatic extraction (AEE) was evaluated during the process of obtaining oil from mamey sapote seed (OMSS). Viscozyme L enzyme complex was used at pH 4 and 50 °C during the optimization of the extraction process by central composite design and response surface methodology. Optimal conditions were: 3.5% (w/w) of enzyme (regarding the seed weight), 5.5 h of incubation time, 235 rpm of agitation rate, and 1:3.5 of solid-to-liquid ratio. These conditions enabled us to obtain an OMSS yield of 66%. No statistically significant differences were found in the fatty acid profile and physicochemical properties, such as the acid and iodine values and the percentage of free fatty acids, between the oil obtained by AEE or by the conventional solvent extraction (SE). However, the oxidative stability of the oil obtained by AEE (11 h) was higher than that obtained by SE (9.33 h), therefore, AEE, in addition to being an environmentally friendly method, produces a superior quality oil in terms of oxidative stability. Finally, the high oil content in mamey sapote seed, and the high percentage of oleic acid (around 50% of the total fatty acid) found in this oil, make it a useful edible vegetable oil.