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Gold extraction from the rock is generally carried out using mercury. However, the high toxicity of mercury has a very dangerous impact on the environment and health. Various efforts have been made to reduce the use of mercury in gold extraction, one of which is the leaching method using thiosulphate and thiourea solution because they have low toxicity and are environmentally friendly. This study aimed to determine the results of gold extraction with thiosulphate and thiourea solution and determined the optimum concentration and time of extraction. The yield of the gold extract with thiosulphate solution was greater than that of thiourea solution. The thiosulphate solution had an optimum concentration of 0.3 M and an optimum time of 2 h. While the thiourea solution had an optimum concentration of 0.2 M and an optimum time of 3 h. The results of the Friedman test on the leaching time and concentration parameters show that leaching time has a significant effect on the Au leaching process, and the concentration parameter does not affect the Au leaching process from solid samples.

[Display omitted] • The rGO/CuI nanocomposites were successfully synthesized via single step co-precipitation methods. • The rGO/CuI-modified GCE was developed for determining trace level concentrations of CAP. • The sensor based on rGO/CuI-modified GCE enhanced its electrocatalytic activity and sensitivity towards CAP detection. • The present sensor was performed to detect CAP with a limit of detection of 8.6 nM. • The rGO/CuI-GCE was in acceptable in real sample analysis and good % recovery value. Carbon-nanomaterials-based photoelectrochemical sensors have received attention and become promising methods in analytical techniques due to their unique benefits, such as easy fabrication, high sensitivity, and selectivity. Herein, the rGO/CuI-modified glassy carbon electrode (rGO/CuI-GCE) has been fabricated to enhance the sensitivity detection of chloramphenicol (CAP). The rGO/CuI was synthesized using the co-precipitation method, while the rGO/CuI-GCE was fabricated using a dropping technique on the GCE surface. The properties of rGO/CuI were studied by x-ray diffraction (XRD), fourier transform infrared (FTIR), raman spectroscopy, UV–Vis spectroscopy, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Furthermore, using a three-standard electrode, the photoelectrochemistry of rGO/CuI-GCE was studied by observing the photocurrent response to time (i vs t). Under optimal conditions, the rGO/CuI-GCE sensor presented significant CAP detection performance in the 0–40 uM with a detection LOD of 8.6 nM (S/N = 3). The sensor also has good stability and selectivity. In addition, the developed sensor was successfully applied to detect CAP in fresh milk and urine with a good % recovery value. The developed photoelectrochemical sensor based on rGO/CuI-modified GCE offers a promising approach for enhancing the sensitivity detection of CAP and others. [ABSTRACT FROM AUTHOR]