Categoría 2

The second methodology as outlined previously has some significant modifications based on the first methodology. However, the beginning preparation of the volcanic ash sample remained consistent throughout the nine samples that were tested. This methodology was used with the remaining eight volcanic ash samples. The main modification in this second methodology is how the leachates were sampled. Instead of pumping from the boiling flask, the Soxhlet apparatus was modified so that the heater was placed on a laboratory jack. This methodology was designed to prevent the problems with breaking boiling flasks through thermal shock as was found in the first methodology. Some of the specificatons on the first methodology remained the same, especially in the preparation phase. As in the first

methodology, the first step was to fill the 250ml boiling flask with 250ml of deionised water and then put it in the fume hood to reach boiling point. Also another boiling flask was filled with 250ml of deionised water at room temperature as was done with the initial Time 0 in the first methodology. This boiling flask was placed in the Soxhlet underneath the three-way intersection and tightened with a clamp. The laboratory jack, which was in the down position, was then wound up so that the aluminium hotplate sat snug against the boiling flask. Note that only one heater (the new Thermolyne, Type 1000 heater) was used in this methodology. The heater was set to a dial setting of 6, as this corresponded to a temperature of 20°C water dripping into the sample using a thermocouple, Figure 8.

The initial Time 0 sample was treated in the same way as in the first methodology where it was collected separately and the time of sampling dictated subsequent samples. However, the time regime sampling was changed slightly where instead of something every cycle in the first hour sampling on the first day it was done once every hour after Time 0 to 6 hours. The sampling regime continued normally once daily as in the first methodology. However, as mentioned previously collecting the samples was different. When our sampling cycle had completed and it was time to sample, the first task was to wind down the laboratory jack isolating and

separating the heat and thus stopping the cycle, Figure 9. Then using a thick wool glove the boiling flask was removed after undoing the clamp and placed in a 500ml beaker filled with cold tap water. This was a two-fold function, first to cool down the sample, and secondly to serve as a holder before the well-known next step was completed. The next step was to remove the two layers of tinfoil that acted as insulation which in turn acted to increase efficiency of heating. Again, using the wool glove a fresh sample was collected and preheated from the fume. This was placed in the Soxhlet reactor in the same identical method as was the first time 0 sample – the only difference was that this sample was already preheated. The

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laboratory jack was then wound back up and the cycle allowed to proceed. The last step was to replace the two layers of tinfoil around the boiling flask in the soxhlet reactor which had been removed.

2.314 Sampling regime over experimental time via time

The sampling regime for the first methodology had an emphasis on time. For the first 2 hours of sampling the brine, the frequency was for every cycle. Therefore, it was essential for maximum efficiency and turnaround time to have as many 250ml boiling flasks with fresh samples being pre-boiled. While this step ensured the cycles were kept timed for the 2 hours keeping up with the demanding regime sometimes resulted in mistakes being made. This is the case with the first methodology when the Sakurajima volcanic ash was trailed because there were two Soxhlets going at the same time. The probability of unforced errors increased with the demands of two Soxhlets to sample. Although in theory spacing the two Soxhlets 10 minutes apart should have prevented any double-ups, but the faster running time of the old heater made this a repeating recurrence. This rapid sampling regime made it vulnerable to

Extra insulation plus zip tie added (right- hand side)

Figure 8: The thermocouple used in monitoring the temperatures of the water dripping into the Soxhlet reactor holding the volcanic ash sample.

Figure 9: Two different methodologies, 1st on the left, modified 2nd _{methodology on the}

right. Note, Black line shows the 10cm needed to raise the modified methodology.

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missing sampling. In fact, on the first day that thefirst methodology was tried, mistakes were made to the degree where the data could not be considered for this experiment.

Once the two hours were concluded the sampling frequency decreased significantly. In the first methodology sampling took place in the succeeding 2, 3, 4 and 6 hours after the first Time 0 cycle had been sampled. Then sampling was done on a daily basis until the total 168 hour time was completed. However, the frequency of the sampling could not be extended more than 24 hours apart. A continuing loss of sample occurred to the extent that the final brine sample ended losing 150-100ml of water over 24 hours. Therefore, decreasing the frequency between sampling would have resulted in a complete loss of sample. During the second methodology (Figure 12), the sampling regime was modified during the first day. From 24 hours onwards, the brine sampling regime remained identical.

After each sampling of the soxhlet reactors when it was convenient the pH as well as the electrical conductivity was measured. First, the samples were removed from the chiller room where they were stored temporarily. The samples were then allowed to warm to room temperature before any analysis had begun. The electrical conductivity is a direct measure of the dissolved salts that may be present in the sample. In this experiment a Hanna Instruments HI 2300 EC/TDS/NaCl meter was used. The probe for this instrument is a little different in that it does not sit in any solution, rather it is left in open air. This was the first meter used before the pH meter, because the pH probe leaches Cl- to obtain a soluble pH reading. The radiometer analytical model: PHM210 interlab was the standard pH meter that was used. This was also one of the reasons that one of the P35 35ml containers of sample was kept apart specifically to measure the electrical conductivity and the pH. In the case of measuring the Soxhlet samples, it was in the period before the measuring for the Ion Chromatography.