[001] Introduction

[002] Phosphate is a critical nutrient necessary for adequate plant growth and is commonly used as a fertilizer in the agricultural industry. Due to this, the rate of phosphate mining greatly increased in the last century. Phosphate minerals on the Earth are limited, phosphate is generally mined from phosphate minerals called phosphorite, and projections suggest that at the current rate of consumption phosphorus is estimated to run out in ~ 300 years. [1] Overapplication of phosphate (over fertilization) also contributes to toxic red algae blooms that result from phosphate baring agricultural runoff. Due to this, phosphate is considered an area where humanity has exceeded the relevant planetary boundary, a condition that describes the overall health of planetary earth systems such as biochemical flows (which includes phosphate). [1] This highlights the urgent need to find cost-effective ways to 1) recover phosphate from various sources: industrial and municipal phosphate -rich wastewaters, and ag-runoff from over fertilized agricultural sectors, and 2) deliver the recovered phosphate in a targeted and controlled manner to agriculture and farm sectors.

[003] Summary of the Invention

[004] The invention provides methods and compositions comprising modified bauxite for phosphate recovery and recycling.

[005] In an aspect the invention provides a method of adsorbing phosphate from a source medium, comprising contacting the source medium comprising phosphate with bauxite under conditions wherein the bauxite absorbs the phosphate.

[006] In embodiments:

[007] the bauxite is mildly processed bauxite (MPB), thermally activated bauxite (TAB), or acid treated thermally activated bauxite (ATAB);

[008] the medium comprises an initial phosphate concentration of 5 ppm to 631 ppm;

[009] the method achieves an initial to final phosphate medium concentration ratio of at least 2, 5, 10, 20 or 50;

[010] the medium is industrial or municipal wastewater, agricultural runoff, animal husbandry wastewater, or other freshwater bodies (e.g., streams, rivers), such as those contaminated with the previously mentioned phosphate-bearing media;

[Oil] the medium is separated urine, wherein the method provides adsorptive capture of phosphate from urine with bauxite; [012] the method comprising delivering the bauxite (without pre-loading it with phosphate) to soil, and delivering (e.g. by pulse delivery) the phosphate to the soil either contemporaneously or after delivering the bauxite, wherein the bauxite then acts as a phosphate sponge, adsorbing excess phosphate, to reduce run-off or seepage into groundwater, and slowly releasing the phosphate to plants I crops as their root systems demand it; and/or

[013] the method further comprising delivering the phosphate-adsorbed bauxite to a planting medium, such as an agricultural soil, such as wherein the phosphate-adsorbed bauxite is in form of phosphate-preloaded pellets for controlled release of the phosphate;

[014] In an aspect the invention provides a method of delivering phosphate to a planting medium, comprising contacting the medium with phosphate-adsorbed bauxite under conditions wherein the bauxite releases the absorbed phosphate;

[015] In embodiments:

[016] the medium comprises an agricultural soil; and/or

[017] the phosphate-adsorbed bauxite is in form of phosphate-preloaded pellets for controlled release of the phosphate;

[018] In an aspect the invention provides a composition comprising phosphate-adsorbed bauxite in a source medium;

[019] In embodiments:

[020] the bauxite is mildly processed bauxite (MPB), thermally activated bauxite (TAB), or acid treated thermally activated bauxite (ATAB);

[021] the medium comprises an initial phosphate concentration of 5 ppm to 631 ppm;

[022] the medium comprises an initial to final phosphate medium concentration ratio of at least 2, 5, 10, 20 or 50;

[023] the medium is industrial or municipal wastewater, agricultural runoff, animal husbandry wastewater, or other freshwater bodies (e.g., streams, rivers), such as those contaminated with the previously mentioned phosphate-bearing media;

[024] the medium is separated urine, wherein the method provides adsorptive capture of phosphate from urine with bauxite; and/or

[025] In an aspect the invention provides a composition comprising phosphate-adsorbed bauxite in a planting medium.

[026] In embodiments:

[027] the medium is agricultural soil; and/or

[028] the phosphate-adsorbed bauxite is in form of phosphate-preloaded pellets for controlled release of the phosphate. [029] The invention encompasses all combinations of the particular embodiments recited herein, as if each combination had been laboriously recited.

[030] Brief Description of the Drawings

[031] Fig i. Isotherm plot of adsorption density vs equilibrium phosphate concentration using acid-treated thermally activated bauxite (ATAB). Isotherm demonstrates Freundlich adsorption behavior (dotted line) and yields a calculated maximum adsorption capacity of 50.04 mg PC ’/g ATAB.

[032] Fig. 2. Isotherm plot of adsorption density vs equilibrium phosphate concentration using thermally activated bauxite (TAB). Isotherm demonstrates Langmuir linear-partition adsorption behavior (dotted line) and yields a calculated maximum adsorption capacity constant of 25 mg PO ₄ 7g TAB.

[033] Fig. 3. Average phosphate remaining (mg/L as P) at various thermally activated bauxite loadings (g/L). Synthetic fresh urine was used in all these experiments. Desired amounts of TAB were added to the synthetic urine solution and mixed continuously. Phosphate remaining at various mixing times (or contact time) are shown in this plot. The recipe for synthetic urine obtained from Larsen, Tove A., et al. "State of the art of urine treatment technologies: A critical review." Water Research X 13 (2021): 100114).

[034] Description of Particular Embodiments of the Invention

[035] Unless contraindicated or noted otherwise, in these descriptions and throughout this specification, the terms “a” and “an” mean one or more, the term “or” means and/or. It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents, and patent applications cited herein, including citations therein, are hereby incorporated by reference in their entirety for all purposes. [036] The invention provides cost-effective and carbon-friendly methods and compositions to 1) recover phosphate from various sources, such as industrial and municipal phosphate -rich wastewaters, and ag-runoff from over fertilized agricultural sectors, and 2) deliver phosphate in a targeted and controlled manner to agriculture and farm sector.

[037] Bauxite is one of the most abundant natural ores on Earth, and one of the cheapest with mined bauxite costing about $40/tonne. Compared to the industry standards used for phosphate recovery, activated magnesia and activated alumina, which cost $2250 and $2000 per tonne respectively, bauxite is very inexpensive. Further, owing to the very large carbon emissions associated with the production of activated magnesia and activated alumina, [2] the use of bauxite in their place is highly attractive because a phosphate adsorbents prepared with bauxite requires little to no chemical processing. [2] The bauxite-derived adsorbents are made even more attractive when you consider the maximum adsorption capacity constants for activated magnesia and activated alumina, reported to be 25 mg PO4-/g and 11 mg PO4-/g, respectively, at pH=6. The value for TAB is 25 mg PO4-/g at pH=6, and the value of AT AB is 50 mg PO4-/g at pH=6. [3] We note that these values are obtained as constants from the fitting of experimental data with isotherm equations and do not represent, the absolute limit of phosphate loading onto our materials. For instance, given the linear nature of TABs isotherm, the amount of loading onto TAB scales linearly with the amount of free phosphate in solution within practical values relevant to our applications.

[038] Another highly active phosphate adsorbent that may show competitiveness with AT AB and TAB is activated red mud, [4] which is reported to show an adsorption capacity constant of -200 mg/g. While this value is excellent, it is important to note that red mud is a waste product from the environmentally harmful Bayer Process, used to extract alumina from bauxite for the manufacture aluminum. This presents limitations on the use of red mud for widespread adoption as a phosphate capture agent. Naturally, its availability is limited to locations where aluminum is being produced. Unlike these places, bauxite (our raw material) is widely dispersed in the Earth’s crust, and would not require commitment to large transportation costs that would be associated with red mud. Further, the red mud adsorption product reported in [4] requires roasting at 700-900 °C for it to function as an active adsorbent, whereas our materials require temperatures of only 300 °C.

[039] Advantages of the invention include 1) cheaper than all commonly used industrial standard adsorbents, 2) more carbon friendly than industrial standard adsorbents, 3) environmentally friendlier (because of little to no chemical processing), and 4) with equal or better capacity for phosphate adsorption than industrial standard materials. The invention provides benign low-cost products and methods, with no adverse environmental effects.

[040] We have validated multiple different forms of bauxite to be effective adsorbents for phosphate ions: 1) Mildly processed bauxite (MPB), which is essentially ball-milled raw bauxite ore; 2) Thermally activated bauxite (TAB), which is ball-milled bauxite ore subjected to 300 C roasting, and 3) Acid treated thermally activated bauxite (ATAB), which is ball-milled bauxite ore subjected to 300 C roasting and subsequent acid treatment using 5M HC1.

[041] These three different forms of bauxite are shown to adsorb phosphate in high amounts from solutions containing a range of initial phosphate concentrations, 5 ppm to 631 ppm. For example, AT AB shows the highest adsorption density, demonstrating a value of 50 mg of PO4- /g AT AB at pH=6

[042] TAB shows an adsorption density of 25 mg PO4-/g TAB at pH=6. There are two industry standard materials for phosphate adsorption, activated magnesia (MgO), and activated alumina (A12O3). For comparison activated magnesia (MgO) demonstrates an adsorption capacity of 25 mg PO4-/g at pH=6. Activated alumina (A12O3) shows an adsorption capacity of 11 mg PO4-/g at pH=6 (reference: Journal of Environmental Chemical Engineering 5 C(2017) 3181-31893183).

[043] The invention provides a low-cost, high capacity, benign P adsorbent that can be easily manipulated by plants (via root-exudates or root-zone bacterial community) to release its P content. The invention provides simple, non-toxic, cost-effective recycling P from wastewater back to the farmland, targeted delivery of P to plant roots to use less P and reduce agricultural runoff which causes P pollution.

[044] Practical applications include: 1) Large scale treatment of wastewaters from industrial sources to capture phosphate; 2) Treatment of municipal wastewaters that contain elevated phosphate levels from urine; 3) Use as a phosphate-preloaded pellets for controlled release of phosphate to plants; 4) phosphate scavenger at agricultural sites to recover excess-phosphate from agricultural -runoffs, from over fertilization.

[045] Practical embodiments include: 1) Column based adsorption for directed water treatment to remove phosphate loading of wastewater discharge; 2) preloading of adsorbent pellets for controlled release of phosphate as fertilizer, 3) incorporation into composite electrode for electrochemically-assisted phosphate removal, 4) batch process by mixing the adsorbent, for treatment of site-specific waters for phosphate capture.

[046] Table 1. Values obtained from adsorption studies using ATAB (see Fig. 1) [047] Table 2. Values obtained from adsorption studies using TAB (see Fig. 2)

[048] References:

[049] [1] Science 13 Feb 2015: Vol. 347, Issue 6223, 1259855 DOI: 10.1126/science.1259855

[050] [2] ACS Sustainable Chem. Eng. 2019, 7, 22, 18323-18331

[051] [3] Journal of Environmental Chemical Engineering 5 (2017) 3181-31893183

[052] [4] Journal of Environmental Sciences 19 (2007) 1166-1170