Permeability and Adsorption–Desorption Behavior of Rare Earth in Laboratory Leaching Tests

In order to investigate the influence of the ion exchange process on the permeability of rare earth ore bodies in the leaching process, a laboratory-scale comparative experiment with ammonium sulfate solution and deionized (DI) water as leaching solutions is conducted. Compared with the DI water leaching test, the permeability coefficient of the rare earth ore sample leached by the ammonium sulfate solution gradually decreases at the beginning and then increases with the completion of leaching. The physical and morphological evolutions of rare earth ore samples in this comparative experiment are also monitored by nuclear magnetic resonance and scanning electron microscopy. It is concluded that the change in the permeability coefficient arises from the adsorption–desorption of a large number of clay microparticles, resulting in a dynamic evolution of pore structures. Further mechanism analysis suggests that the change in internal ionic strength caused by ion exchange and leaching solution seepage promotes the adsorption–desorption behavior of clay microparticles.

The Novel Strategy for Increasing the Efficiency and Yield of the Bipolar Membrane Electrodialysis by the Double Conjugate Salts Stress

To improve sulfuric acid recovery from sodium sulfate wastewater, a lab-scale bipolar membrane electrodialysis (BMED) process was used for the treatment of simulated sodium sulfate wastewater. In order to increase the concentration of sulfuric acid (H2SO4) generated during the process, a certain concentration of ammonium sulfate solution was added into the feed compartment. To study the influencing factors of sulfuric acid yield, we prepared different concentrations of ammonium sulfate solution, different feed solution volumes, and different membrane configurations in this experiment. As it can be seen from the results, when adding 8% (NH4)2SO4 into 15% Na2SO4 under the experimental conditions where the current density was 50 mA/cm2, the concentration of H2SO4 increased from 0.89 to 1.215 mol/L, and the current efficiency and energy consumption could be up to 60.12% and 2.59 kWh/kg, respectively. Furthermore, with the increase of the volume of the feed compartment, the concentration of H2SO4 also increased. At the same time, the configuration also affects the final concentration of the sulfuric acid; in the BP-A-C-BP (“BP” means bipolar membrane, “A” means anion exchange membrane, and “C” means cation exchange membrane; “BP-A-C-BP” means that two bipolar membranes, an anion exchange membrane, and a cation exchange membrane are alternately arranged to form a repeating unit of the membrane stack) configuration, a higher H2SO4 concentration was generated and less energy was consumed. The results show that the addition of the double conjugate salt is an effective method to increase the concentration of acid produced in the BMED process.

Synthesis of Cross-Linked Poly(acrylamide) Microspheres by Dispersion Polymerisation in Aqueous Ammonium Sulfate Solution

Cross-linked poly(acrylamide) microspheres, i.e. PAMBA, with mean diameters ranging from 169.7 to 525.2 nm were prepared by dispersion polymerisation of acrylamide in aqueous ammonium sulfate (AS) solution. N,N′-methylenebis(acrylamide) (MBA), sodium dodecyl sulfate (SDS), and potassium persulfate (KPS) were selected as the cross-linking agent, stabiliser, and initiator, respectively. The basic conditions for producing PAMBA microspheres, such as the salt concentration and monomer concentration, were optimised based on the precipitation behaviour of the polymer and the state of the product obtained after polymerisation. The optimum AS concentration and monomer concentration were determined as 300 and 88 g L−1, respectively. The effects of parameters, such as SDS concentration, MBA concentration, initiator concentration and temperature, on the product morphology and particle size were investigated by dynamic light scattering and transmission electron microscopy. The results show that the optimum conditions for the generation of microspheres are concentrations of 2.2–8.8 g L−1 for SDS, 4–6 g L−1 for MBA, 0.3–1.0 wt-% based on acrylamide for KPS, and the temperature should be kept at 35–45°C. The mean diameter of the microspheres decreases with an increase in SDS concentration and increases with an increase in MBA concentration. The polydispersity of the microspheres increases when SDS concentration exceeds 6.6 g L−1 as well as when MBA concentration increases. The formation mechanism of the products was discussed based on the results.

What is the effect of ammonium sulfate on the heart rate of Daphnia magnia?

Ammonium sulfate [(NH4)2SO4] is one of the most widely used nitrogen-based fertilizer in agriculture, and has been produced for over 150 years. However, limited research has been done to investigate the eco-toxic effects of ammonium sulfate, commonly present in surface runoff. This study therefore aimed to investigate the effects of varying ammonium sulfate concentrations on the normal physiology of Daphnia magna through a modified acute toxicity testing. Concentrations of ammonium sulfate solutions at 0M, 0.05M, 0.10M, 0.15M, 0.20M, 0.25M, and 0.30M were prepared and tested on 10 D. magna for each concentration of ammonium sulfate solution. The bioassay test was done by observing the effects of different concentrations of ammonium sulfate solution on the heart rate of D. magna. The percentage increase in average heart rate of D. magna after exposure to the respective concentrations of ammonium sulfate solution were calculated and a relationship between varying concentrations of ammonium sulfate concentration and the heart rate of D. magna was illustrated by plotting a graph using the respective data points obtained. Results indicated that increasing concentrations of ammonium sulfate solution resulted in an increase in the heart rate of D. magna per minute, up till 0.20M concentration. Increasing concentrations of ammonium sulfate solution beyond 0.20M resulted in a decrease in the heart rate of D. magna per minute. It was also discovered that specifically, the ammonium ions present when ammonium sulfate dissociates in water, is responsibility for toxicity, and not the sulfate ions. It is reasonable to conclude that ammonium sulfate poses significant eco-toxic effects as D. magna is a common primary consumer in many freshwater aquatic ecosystems, any change in its population quality or quantity can cause irreparable effects to the populations of other aquatic organisms.