Geochemical CompGeochemical Comparison of Fresh and Weathered Tailings from the Sabodala Gold Mine Kedougou Region, Senegal Following 6 Years of Operationarison of Fresh and Weathered Tailings from the Sabodala Gold Mine Kedougou Region, Senegal Following 6 Years of Operation

The Sabodala gold mine is located in the Kedegou region in eastern Senegal near the border with Mali in a tropical Savannah climate zone with distinct wet and dry seasons. The mine has been operating since 2009 with active tailings deposition giving an ideal opportunity to study the weathering characteristics of carbonate rich tailings materials under real world conditions. The mine is operated in accordance with international best practice with regular monitoring of water quality and tailings chemistry in accordance with the international cyanide management code (ICMC) and also in order to monitor and control any potential impacts from Acid Rock Drainage and Metal Leaching (ARDML) that may be generated from the tailings materials and waste rock. In 2015 as part of a project looking at the potential for re-use of generated tailings as construction materials, a number of additional geochemical tests including whole rock assays, mineralogy, Acid Base Accounting in accordance with modified Sobek method with siderite correction, together with paste pH and electrical conductivity (Ec) measurements were undertaken. The purpose of the study was to update the predictions of the potential for ARDML generation and drainage pH in leachates forming from the Sabodala tailings. The tests were run on one composite weathered and 3 selective fresh samples collected by auger drilling on three holes over the tailing. Results have enabled a better understanding of the chemical weathering characteristics of finely ground tailings materials under tropical weathering conditions and the nature of secondary minerals precipitated.

A Study of DTC-Power Electronic Cascade Fed by Photovoltaic Cell-Three-Level NPC Inverter

This paper proposes a high performance three-level inverter Neutral Point Clamped (NPC) structure for photovoltaic system. The proposed configuration which can boost the low voltage of photovoltaic (PV) array, can also convert the photovoltaic DC power into high quality AC power. Attention has been paid to the problem of neutral point potential variation. In this way, a Direct Torque Control (DTC) technique has been applied and the estimated value of the Neutral Point Potential (NPP) is used, which is calculated by motor currents. This control strategy uses the redundancy presented by the inverter for selecting appropriate switching state through a switching table to achieve the control of NPP. This study shows the effect of the stability problem of the DC voltages and good static and dynamic performances were obtained in simulation of the proposed cascade “photovoltaic cell-three-level NPC VSI-induction motor”.

Energy neutrality potential of wastewater treatment plants:A novel evaluation framework integrating energy efficiency and recovery

Wastewater treatment plants(WWTPs)consume large amounts of energy and emit greenhouse gases to remove pollutants.This study proposes a framework for evaluating the energy neutrality potential(ENP)of WWTPs from an integrated perspective.Operational data of 970 WWTPs in the Yangtze River Economic Belt(YREB)were extracted from the China Urban Drainage Yearbook 2018.The potential chemical and thermal energies were estimated using combined heat and power(CHP)and water source heat pump,respectively.Two key performance indicators(KPIs)were then established:the energy self-sufficiency(ESS)indicator,which reflects the offset degree of energy recovery,and the comprehensive water–energy efficiency(CWEE)indicator,which characterizes the efficiency of water–energy conversion.For the qualitative results,98 WWTPs became the benchmark(i.e.,CWEE=1.000),while 112 WWTPs were fully self-sufficient(i.e.,ESS≥100%).Subsequently,four types of ENP were classified by setting the median values of the two KPIs as the critical value.The WWTPs with high ENP had high net thermal energy values and relatively loose discharge limits.The explanatory factor analysis of water quantity and quality verified the existence of scale economies.Sufficient carbon source and biodegradability condition were also significant factors.As the CWEE indicator was mostly sensitive to the input of CHP,future optimization shall focus on the moisture and organic content of sludge.This study proposes a novel framework for evaluating the ENP of WWTPs.The results can provide guidance for optimizing the energy efficiency and recovery of WWTPs.