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The Formation of struvite Scale Formation and the Effect of As(V) and Hg(II) Impurities

Picture for The Formation of struvite Scale Formation and the Effect of As(V) and Hg(II) Impurities
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Magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O Struvite) scale deposits is often a serious operational problem in anaerobic treatment of municipal waste water and other industrial wastewaters. The kinetics of the nucleation and crystal growth at conditions simulating municipal wastewater was investigated in a 1L reactor at conditions of constant supersaturation at pΗ 9.50 25°C both in the absence and in the presence of As(V) and Hg(II) at concentration levels precluding the formation of insoluble salts of these impurities. Over the range of the relative supersaturation with respect to struvite investigated (σ=0.096-0.37) the presence of As(V) resulted in lower rates of crystal growth while the mechanism was the same in both cases i.e. surface diffusion controlled. The effect of As(V) concentration on the crystal growth rates of struvite was diminished as the supersaturation increased. The presence of As(V) at concentrations in the range 0.1-1 mM resulted in 90% reduction of the rates of crystal growth while induction times increased significantly. The presence of Hg(II) resulted in acceleration of the rates of crystal growth while no induction times were observed. In both cases equilibrium adsorption measurements showed that the effect of As(V) and Hg(II) is due to the interaction of these ions with the surface of the growing supercritical struvite nuclei.

Product Number: 51319-12942-SG
Author: Petros Koutsoukos
Publication Date: 2019
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Picture for 07057 STRUVITE SCALE FORMATION AND INHIBITION IN WASTEWATER
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07057 STRUVITE SCALE FORMATION AND INHIBITION IN WASTEWATER

Product Number: 51300-07057-SG
ISBN: 07057 2007 CP
Author: Petros G. Koutsoukos and Aikaterini N. Kofina
Publication Date: 2007
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Picture for Electrochemical Corrosion Behavior of Carbon Steel With and Without Residual Elements
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Electrochemical Corrosion Behavior of Carbon Steel With and Without Residual Elements

Product Number: 51320-14245-SG
Author: Suresh Divi, Sri Krishna Chimbli
Publication Date: 2020
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Residual elements (RE) in carbon steel, not specifically included in the specified steel, appear to influence the corrosion rate under certain conditions, especially in services involving hydrofluoric acid (HF). The relative proportions of RE, specifically %C, %Ni, %Cu, and %Cr in carbon steel base and weld metals used in refineries, especially in alkylation processes with HF as the catalyst, significantly impact corrosion behavior. Studies described in the literature show corrosion damage with high RE (Cu + Ni + Cr >0.20) components as compared to low RE (Cu + Ni + Cr <0.20) components.  

In this study, electrochemical corrosion testing was performed on a 3-inch pipe elbow section with high REs that had developed a through-wall leak in service. Test results were compared to those obtained on a similar pipe elbow section with lower REs. The samples were exposed to 50% HF at room temperature and at 65°C. Linear polarization resistance (LPR) corrosion rates were measured at both temperatures. Potentiodynamic (PD) polarization scans were performed on samples of low and high RE steel exposed to 50% HF at room temperature.  

Test results indicated that LPR corrosion rates were higher for the high RE carbon steel samples than for low RE carbon steel samples at both temperatures. PD scans showed that the critical current densities were higher for high RE steel than for low RE steel.  
Picture for Effects of Minor Alloying Elements on the Metal-Dusting Behavior of Ni-Based Alloys
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Effects of Minor Alloying Elements on the Metal-Dusting Behavior of Ni-Based Alloys

Product Number: 51320-14657-SG
Author: Bingtao Li, Wei-Ting Chen, Brian Gleeson, Heike Hattendorf
Publication Date: 2020
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Alloys are often found to suffer much greater metal-dusting attack under high-pressure conditions compared to ambient-pressure conditions. Ultimately, the resistance of a given alloy to metal dusting depends on the formation of an oxide scale that is impermeable to carbon which, in turn, depends on scale composition and structure. This paper reports the metal-dusting behavior of several Ni-based alloys having relatively high Cr contents (about 30 wt.%) and different controlled minor levels of Fe, Al, and/or Si. Testing was conducted under 20 bar total pressure of a high-carbon-activity gas at 600 °C (1112 °F). The exposed alloys were analyzed by SEM and TEM techniques to evaluate the oxide scales and evidence of carbon ingress. It was found that aluminum is beneficial to improve metal dusting resistance by reacting to form a continuous inner layer of alumina; whereas iron is detrimental to resistance. Mechanistic aspects of the role(s) played by minor elements in affecting metal-dusting resistance are considered.  
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