Tds meter

In order to investigate the concentration of impurities in PG and backfill samples, the toxicity leaching test was conducted according to HJ 557-2010. After curing for 28d, the backfill samples were grounded and sieved through a 3.0 mm screen. The powders were mixed with deionized water in a container at a mass proportion of 1:10 and shaken at 110 rpm/min on a rotary shaker for 8 h. Then the mixtures were placed on the table for 16 h. Finally, the mixtures were filtered through a 0.45 mm filter, and the leachates were collected for further analysis.
The pH value of PG, bleeding water and the leachate of toxicity leaching test was measured by pH meter (Ohaus, US). The concentrations of SO₄²⁻ and PO₄³⁻ were determined by ammonium molybdate tetrahydrate spectrophotometry (Shimadzu, Japan). The total dissolved solids (TDS) and the concentration of F⁻ were measured by TDS meter (Ohaus, US) and fluorine ion-selective electrode (Leici, China), respectively.

The toxic leaching test was conducted to evaluate the quantities of impurities in the PG used in this study according to Chinese standard HJ 557-2010 [38 ]. The three batches of PG (dry mass) and deionized water were mixed in a ratio of 1:10. The mixture was put on a horizontal shaker to shake at 110 rpm/min for 8 h and then was moved to a table for 16 h. The supernatant was collected and filtered through a 0.45 mm filter for further analysis. The concentrations of PO₄³⁻ (as mg/L P) and SO₄²⁻ in bleeding water were measured with a spectrophotometer (Shimadzu, Japan). The concentration of F⁻ was measured using a fluorine ion-selective electrode (Leici, Shanghai, China). The pH and total dissolved solids (TDS) were tested using a pH meter (Ohaus, Parsippany, NJ, USA) and a TDS meter (Ohaus, Parsippany, NJ, USA), respectively.