DOI: 10.5285/b8aa3ec7-e539-4255-a21a-0c780fbf89f6
title: Geochemical products of laboratory-simulated abrasion of natural quartz and alkali feldspar incubated at low temperatures

description: Geochemical data collected during a 40 day incubation of crushed silicate minerals (quartz and alkali feldspar). Quartz and alkali were crushed separately under an oxygen-free atmosphere using a planetary ball mill. The crushed minerals where then incubated in serum vial under with oxygen-limited water, in an oxygen-free N2 atmosphere at 4 degrees C. Headspace gases were collected before the addition of water. Then, headspace gas samples and the water samples were collected 24, 48, 120, 240, 360 and 720 hours after the addition of water. Headspace gas samples were analysed for CH4, CO2 and H2 and O2. Water fraction samples were analysed for anions and organic acids (including acetate, formate, F-, Cl-, NO2-, NO3- and SO4 2-), cations (including Na+, K+, Mg2+ and Ca2+) and total dissolved iron (dFe).

The research was supported by NERC grant NE/S001670/1, CRUSH2LIFE (BGO, MT, JT) and by European Research Council (ERC) Synergy Grant DEEP PURPLE under the European Union's Horizon 2020 Research and Innovation Program (Grant Number 856416).
description: 1. Sample preparation and dry crushing
Quartz (Madagascar) and alkali feldspar (Norway) samples purchased from the Geology Superstore (http://www.geologysuperstore.com) were washed with 18.2 megaohm cm-1 water and dried at 75 degrees C for over 18 hours. Minerals were then wrapped in several layers of paper roll (to avoid metal-rock interaction) and broken down using a sledgehammer on a metal plate. Crushed feldspar samples were washed again using 18.2 megaohm cm-1 water, the 63 um to 2 mm size fraction was collected and dried at 100 degrees C prior to furnacing at 450 degrees C for four hours to remove any trace organics. Quartz samples were washed using 18.2 megaohm cm-1 water, the 63 um to 2 mm size fraction was collected and dried at 100 degrees C prior to furnacing at 1000 degrees C for two hours, to remove any organics and in an attempt to remove fluid inclusions (Bray et al., 1991, Kuznetsov et al., 2012). Crushed minerals were then milled under an oxygen-free nitrogen atmosphere (zero grade, BOC), using a Fritsch Planetary Mono Mill Pulverisette 6 at 500 r.p.m. for 30 mins. Roughly 15g of sample were crushed in the ball mill at any one time. Gas samples of the ball mill headspace were taken both before and after milling the samples. This process was repeated 10 times to generate sufficient crushed sample for sacrificial incubations of the minerals. After milling, the minerals were transferred to a Coy Vinyl Anaerobic Chamber (CoyLabs, MI, US), previously flushed repeatedly with zero grade N2 until Oxoid(TM) Resazurin Anaerobic Indicator (BR0055B, Thermo Fisher Scientific Inc) indicated anaerobic conditions. Within this chamber, crushed samples were transferred into a large serum vial, which was sealed with grey butyl rubber stoppers (previously boiled in 1 M NaOH for 1 hour and rinsed 6x with 18.2 megaohm cm-1 water), and crimp sealed. The headspace of the vial was then flushed with oxygen-free-N2 for 2 mins and stored in the dark until incubation.

2. Microcosm experiments
Six x 6 g triplicate samples, one for each time point, were weighed into 50 ml borosilicate serum bottles (previously acid washed, rinsed 6 x with 18.2 megaohm cm-1 water, and furnaced at 450 degrees C for 4 hours). They were placed into an anaerobic chamber which had been repeatedly flushed with N2 until an Oxoid(TM) Resazurin Anaerobic Indicator showed that the headspace was anoxic. The serum bottles were then sealed with thick blue butyl rubber stoppers, previously boiled in 1 M NaOH for 1 hour, soaked in purite overnight and rinsed 6 times with 18.2 megaohm cm-1 water, which in turn were crimp sealed. The sealed vials were flushed for 2 mins with oxygen-free-N2 and stored at 0 degrees C until the addition of water and the start of the incubation experiments. Triplicate blank vials were prepared for each time point following the same methods. Once all vials were crimped and flushed, approximately 8 ml of 18.2 megaohm cm-1 water (flushed with N2 for over an hour) at 0 degrees C were added to each vial.


3. Headspace analysis
Serum bottles were analysed prior to the addition of water by over pressurising the bottles with 10 mL of oxygen-free N2 (zero grade, BOC). A 10 mL headspace gas aliquot was transferred into a 5.9 mL double-wadded Exetainer(R) (Labco, Lampeter, UK) using a gas-tight syringe. Approximately 8 mL of 18.2 megaohm cm-1 water (at 4 degrees C and sparged with oxygen-free N2 for over an hour) was then added to the serum bottles. The headspace in the vials was subsampled after 24 hours following the same method. Headspace samples were then taken at 48, 120, 240, 360 and 720 hours after the addition of water to the vials, following this same procedure. A 5 mL gas subsample was taken from the exetainers and analysed using an Agilent 8860 Gas Chromatograph (Agilent Technologies, Santa Clara, CA, USA). Concentrations of CH4 and CO2 were determined by a Flame Ionization Detector (FID). The sample loop was 0.5 mL, Helium (He) was used as the carrier gas, and a Porapak Q 80-100 mesh, 2 m x 1/8 inch x 2 mm SS column and a methaniser were used to distinguish the compounds. The concentrations of H2 and O2 were determined using a Thermal Conductivity Detector (TCD), using a 1 mL sample loop, Argon (Ar) as the carrier gas, and a Hayesep D 80-100 mesh, 2 m x 1/8 inch SS column, in series with a molecular sieve 5a, 60-80 mesh, 8 ft x 1/8 inch column. The oven temperature was set at 30 degrees C for the initial 4 mins, and then the temperature ramped up at rate of 50 degrees C min-1 until the oven reached a temperature of 200 degrees C. This temperature was maintained for 2.5 mins, when the run was concluded. The concentrations of headspace gases were calculated based on a standard-curve generated from the dilution of a mixed gas. The ideal gas law was used to convert to molar concentrations, and concentrations were corrected for dilution during sampling and for gases dissolved in the water using Henry's Law (where relevant). The results were also blank corrected for each time point and normalised to dry sediment mass.


4. Water chemistry analysis
The vials were opened immediately after gas sampling, and the liquid overlying the sediment was filtered using 0.22 um Sartorius(TM) Minisart(TM) High Flow PES in-line filters. A 5 ml aliquot was used for pH measurements and H2O2 analysis, using DMP (method detailed in Baga et al. (1988) and Gill-Olivas et al. (2021)). 
The remainder of the filtrate was frozen immediately after filtering and stored at -20 degrees C until further analysis for nutrients and organic acids. Anions and organic acids, including acetate, formate, F-, Cl-, NO2-, NO3-, and SO4 2- were analysed using a Dionex ICS 6000, fitted with a Dionex IonPacTM AS11-HC 4 um column. Cations, including: Na+, K+, Mg2+ and Ca2+, were determined using a Dionex IC 5000 fitted with an IonPacTM CS12A 2 mm column.
Total dissolved iron (dFe) was determined by automating and implementing the ferrozine method described in Viollier et al. (2000) on a Gallery Automated Photometric Analyzer.

5. Specific Surface Area
The specific surface area (SSA) of materials was measured using a NOVA 1200e BET Analysis System. Approximately 1 g of dried sample was loaded into a pre-calibrated sample cell. The whole system was then evacuated and dried at 200 degrees C for a minimum of 2 hours (Clausen and Fabricius, 2000). The surface area of materials was measured using nitrogen gas as an adsorbent at 77 K. The system was not calibrated using a certified standard, therefore the values obtained were indicative, rather than absolute.
description: List of instrumentation mentioned in methodology:
Fritsch Planetary Mono Mill Pulverisette 6 (Fritsch Milling and Sizing, NC, USA)
Coy Vinyl Anaerobic Chamber (CoyLabs, MI, US)
Agilent 8860 Gas Chromatograph (Agilent Technologies, Santa Clara, CA, USA)
Dionex ICS 6000 (Thermo Fischer Scientific, MA, US)
Gallery Automated Photometric Analyzer (Thermo Fischer Scientific, MA, US)
NOVA 1200e BET Analysis System (Aanton-Paar, Austria)
description: Concentrations of gases were calculated using a standard-curve generated from the dilution of a mixed gas standard (173738-AH-C, BOC). Standards were run daily and gave a CV of 1.0 % (n = 15) for H2, with a limit of detection (LOD) of 9.6 ppm, equivalent to 4.4 nmol g-1, a CV of 0.8% (n = 15) for CH4, with a LOD of 0.1 ppm, equivalent to 0.04 nmol g-1 and a CV of 0.9 % (n = 15) for CO2, with a LOD of 0.1 ppm, equivalent to 0.05 nmol g-1.
Analysis of anions and organic acids, including acetate (LOD: 1.1 ppb, equivalent to 0.02 nmol g-1; CV: 1.4%), formate (LOD: 0.7 ppb, equivalent to 0.02 nmol g-1; CV: 2.3%), F- (LOD: 1.9 ppb, equivalent to 0.13 nmol g-1, CV: 8%), Cl- (LOD: 1.1 ppb, equivalent to 0.04 nmol g-1, CV: 2.6%), NO2- (LOD: 2.2 ppb, equivalent to 0.06 nmol g-1, CV: 2.2%), NO3- (LOD: 1.8 ppb, equivalent to 0.04 nmol g-1, CV: 1.9%), and SO42- (LOD: 3 ppb, equivalent to 0.4 nmol g-1; CV: 7%) and cations, including: Na+ (LOD: 0.3 ppb, equivalent to 0.50 nmol g-1; CV: 0.3%), K+ (LOD: 0.4 ppb, equivalent to 0.36 umol g-1; CV: 0.6%), Mg2+ (LOD: 1.6 ppb, equivalent to 0.26 umol g-1; CV: 1.0%) and Ca2+ (LOD: 1.1 ppb, equivalent to 0.35 umol g-1; CV: 1.1%).
Total dissolved iron (dFe): LOD of 13 ppb, equivalent to 1.58 nmol g-1.