Nutrient Extraction from Martian Regolith Simulants to Establish Their Suitability as a Substrate for Plant Growth

Education Level

Undergraduate

Faculty Advisor(s)

Professor Stephen O'Shea

Academic Department(s)

Chemistry

Comments

This research was presented at the 2024 Rhode Island Summer Undergraduate Research Symposium, held on Friday, July 26, at the University of Rhode Island and supported by the NASA Rhode Island Space Grant Consortium.

Symposium Date

2024

Abstract

Mars is a prime candidate for future exploration and potential long-term human habitation but presents significant challenges to on-planet sustainable plant growth. Understanding the composition of plants and the essential nutrients they require is crucial for assessing their growth potential on Mars. Terrestrial plants depend on a complex mixture of macronutrients (N, P, K, Ca, Mg, and S) and trace micronutrients (Fe, Mn, Zn, Cu, Mo, B, Cl, and Ni). The Mars regolith is amenable to these nutrients, though lacking carbon, which can be supplemented. The greater challenge is the high levels of toxic perchlorate (2% wt) distributed through the planet's surface, making it unsuitable for plant growth.

To address this challenge, we tested three different Martian soil simulants formulated in Exolith Labs® to explore nutrient extraction on pretreated, perchlorate-removed, regolith. The simulants’ metallo nutrients were extracted by either washing or leaching (2g/(20mls x 5)) with DI water, hydrochloric acid (1M), or acetic acid (1M). These small extraction techniques were then compared to a bulk wash extract (50g/500mls) to see whether a solid stock fertilizer mix could be prepared for growth supplementation of Martian soil similar to the commercial product Jackpot®. Our experimental findings using ICP, FTIR, XRF, and XRD spectroscopy indicate that washing was a more efficient method, and although H2O has limited efficacy in nutrient extraction, HCl and acetic acid solutions significantly enhanced the release of essential nutrients from the simulants. Furthermore, the three simulants were unsuccessful in making a fertilizer mix that contained all of the essential nutrients needed to sustain plant life. However, H2O was the best solution for extracting a mix containing the highest concentration of a number of these essential nutrients.

This study also examined the physical properties of the simulants, including sedimentation rates, water holding capacity, and bulk density. These properties are critical for efficient nutrient extraction and as a potential substrate for viable plant growth. Regolith MGS-1S has the most nutrient-rich regolith as well as the most efficient and timely nutrient extraction because of its high concentration of soluble SO4- anion and larger particle composition. MGS-1 and JEZ-1 have slower extraction efficiencies because their smaller particle size composition allows for greater water holding capacities and slower leach flow.

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